I'm curious to know whether my experience is normal in the United States...

A Canadian here... I have flown many, many miles across Canada and to Europe. I've done a fair amount of air travel across Europe. I have never had any significant itinerary changes in the dozens of itineraries I've flown.

Into the United States, I've flown AA a handful of times and never had any itinerary changes.

However...

For this February, I booked Delta because of a really good itinerary:

YVR-SEA-FLL and FLL-MSP-YVR.

I booked it for several reasons:

* I do not want to find that on our departure date, the entire Eastern Seaboard from Chicago to Halifax is shut down because of a storm.
* My co-traveller is 80 years old and I want to make the trip as least stressful as I can.

Since I booked this itinerary, DL has made the following changes:

YVR-SEA-FLL to
YVR-SEA-DTW-FLL (I moved the departure date to the previous day to keep the original routing)

Then on the return trip, they made a second change:

FLL-MSP-YVR to
FLL-MSP-SLC-YVR

And now tonight, back on the outbound trip (on the earlier day), they've just changed it again!

YVR-SEA-FLL to
YVR-SEA-ATL-FLL

I'm really surprised that I have to stay on top of all these changes to make sure we're still sitting together and stuff like that.

This is really feeling like "bait and switch".

Is this normal these days on all American carriers, or just Delta?

This is not a complaint. But to me anyway, this is completely unprecedented.

What are the thoughts of my more seasoned travellers on A*Net?

I agree, personally I think this is a little ridiculous. I get that schedule changes/equipment swaps happen but to go and completely add another stop into the itinerary, especially the SEA-DTW-FLL which would probably add at least 4-5 hours to your total trip time, is downright misleading and uncalled for. Personally I would call Delta and put your foot down, say you paid for this routing because it was the quickest and most hassle free and now you've been given a completely irrational routing with double-connections and a sidetrack of a few thousand miles. If they can't guarantee your original routing, or at least make it a one-stop, then ask for your money back and be sure to let them know you'll be taking your business to UA or AA. Or ask for a free upgrade to Business or Economy Plus

The only change I've ever had was on AA, they switched my YYZ-CLT-SXM routing to YYZ-MIA-SXM, it actually shortened my itinerary by about 35 mins and we arrived into SXM a little earlier. I was completely okay with that. Seems only US airlines do this as I've never had an itinerary change in a few hundred flights with many airlines in North America and Europe.

I have never flown Delta before but I will be next month. YYZ-ATL-GSO and return the same way, I'm hoping they don't mess with my itinerary because we are scheduled to land in GSO at 11am and I have somewhere to be at 3pm... I am looking forward to knocking off the 717 and MD88 in the same day though. Good luck with the Delta Roulette Game.

Ouch that sounds like no fun to say the least. I had one where I was saving 200 dollars from SFO to TLV 10 years ago, so I decided to do 2 stops. Routing was supposed to be SFO to ORD to MAD to TLV and same on the return. The ticket was Iberia, but first leg on outbound was AA. Mechanical on first flight so trouble already. They rebooked me, SFO-JFK-MAD-TLV. Luckily was leaving at about the same time. I get to MAD to transfer to TLV and I was told that I couldn't be booked on the flight to TLV as it was El AL and that I needed to speak to AA even though I had an IB ticket. So ok, I will talk to AA, one problem have to go through customs to do that. So I go through customs and talk to AA, they say no flights for 2 to 3 days at first. Then they found one that night at 10:30 PM stopping in BCN and on to TLV. So I get a hotel room on my own dime as I have 12 hours. I arrive in TLV the next morning and no luggage. That was delivered later that day. The return was equally bad. Left TLV around 45 minutes late, arrive in MAD and run to my gate, I get there, the airplane is still there attached to the jetway, but I am told I am rebooked as the flight is closed. They send to me a desk and give me a ticket for the next day and put me up at a hotel near the airport. I get to the hotel take a look and realize I am not getting in to SFO until late at night, past midnight. Well i decided to call Iberia and ask to see if I can get in any earlier the next day. The Iberia agent says that I need to go to the airport to do this. I then ask for his supervisor. He comes back a couple minutes later and says my supervisor doesn't want to speak to you. I literally laughed and hung up and just gave up. The next day, i depart MAD arrive in Boston recheck my luggage after going through customs. I arrive in SFO and once again I have no luggage(arrived the next day). So two lessons learned, 1) if you can avoid it, never take two stops and 2) Never fly Iberia.

United has done quite a few schedule switches on me, inevitably with the effect of creating a new 3 hour layover.

American and Alaska take the cake though: they've both cancelled part or all of my itinerary without any warning. I only discovered each of these incidents through accidental diligence. With AA, they scrubbed every BOS-DFW nonstop after 1:15 pm, leaving me with a -4.5 hour connection from my codeshared BA flight. After the customer service agent spent a bit too long trying to find an alternative flight from BOS to DFW, I suggested flying LHR-DFW nonstop, which (thankfully) she did. Of course that flight was cancelled the day of, but that's a different story...

On AS, I was looking up a reservation to check flight times and ran into an ominous error message asking me to call customer service. I rung them up, and yep: when AS launched their PDX-DAL service, they scrubbed the PDX-DFW red eye and didn't tell me at all. Thankfully, that resolution was also simple; I just had to take the red eye out of SEA instead. I still would've liked a notification though!

Several months ago, DL changed my award ticket routing in October of (3 segments) ZAG-AMS-DTW-PDX due to a cancellation of the DTW-PDX flight. I was rebooked on (4 segments) ZAG-AMS-DTW-SLC-PDX. However, a far more logical (3.segments) routing with shorter duration of ZAG-AMS-MSP-PDX existed (with plenty of seats). While a long phone call to DL resulted in that alternative, it seems that either....

1) DL does not automatically offer the shortest duration and fewest connections to customers whose flights have been changed by DL. Surely, many customers simply accept whatever revised itinerary that an airline sends to them.

2) DL does not have adequate systems in place to correctly identify optimized itineraries for these customers.

I've found that DL adjusts flight schedules at least monthly and rarely remain firm until about 45 days prior to departure.
You can anticipate additional changes by DL for your February trip so be don't so quick to rebook everything right now as it likely will change.
I would wait until mid-December and call DL with the latest change you've received to firm up your flight plans.
They are the best to work with by phone and will gladly rebook better connection options particularly if times have changed by more than 90 minutes.
I would suggest you know what the changes are and what new flight schedule you prefer when you call to help the agent assist you.
Be nice and simply ask for their help. They will generally go out of their way to assist you.
As a point of reference. I booked 7 months in advance a TPA-LAX-SYD round with routings all over the place to get to LAX for the one SYD flight.
My itinerary roundtrip changed 11 times in those 7 months and each time an agent patiently rebooked us on alternate flights.
We subsequently rode a nice TPA-ATL-LAX-SYD routing with good times for the roundtrip.

I've found that virtually any itinerary I book on UA more than 2 months out with a stop involved gets changed, sometimes adding an extra stop, sometimes re-timing connections. On one trip, the booking was modified 3 times, one of which took a 1.5 hr connection and turned it into 6 (as in, not even a connection anymore) on the outbound and putting me on a redeye on the return when I'd specifically booked that itinerary because it was NOT a redeye.

It's gotten bad enough that I simply don't fly UA for leisure anymore despite having a mid-tier elite status, even paying extra to fly on others.

I fly a lot on DL, the schedules are forever changing, however I have never had an extra stop put into a routing, give DL a call.

I haven't had anything that absurd, but I have had it happen where my flight changed a number and the times changed very slightly but with the same aircraft type, and yet the change caused my seat assignment to lapse and I had to reselect it. I don't remember the specific airline, but for the sake of argument let's pretend that it would be something like NW 123 MSP-PHX, 2:50 PM to 4:07 PM (A320) becoming NW 1962 MSP-PHX, 2:52 PM to 4:10 PM (A320). This sort of thing happened whenever the airline decided to invent a new "direct" flight number where the designation would actually be something like MKE-MSP-PHX and they'd completely reset the seat map.

Otherwise the worst change I ever had was a NW IAH-MSP flight inexplicably changing from an A319 to a CRJ2 only three weeks before departure, although it was in the air travel doldrums between Thanksgiving and Christmas travel in 2005. At least the CRJ was only a month old at the time but that was still a super uncomfortable downgrade.