Ahhh, UA Shuttle, hmmmmm, what to say.
I'll be honest, my UA Shuttle experiences are limited, and mostly to bad ones.
I first flew them back in '97 when they were getting, I was going on a LAX-PDX flight. It was the Friday of Memorial Day, oh my what a stupid idea! Well, basically the plane left over 3 hours late, full, and boarding took forever with those damn zones. What were they thinking? Probably not much. Anyway, they offered free booze since it was so late, but didn't announce it. Upon arrival the announcement was "Welcome to Portland where the local time is 11.30pm [or something like that]." To which the person sitting in my row on the aisle seat blurts out, "Oh, there is a 3 hour time difference on United." I don't remember the flight coming back.
I've also flown UA shuttle a few times on PDX-LAX and PDX-SFO-BUR when Alaska has cancelled their flights [oh what fun].
I've flown LAX-SFO-LAX. One time the flight up there was delayed 2 hours [twice as long as the flight itself] and the one coming back was cancelled.
I've flown BUR-SFO-BUR once or twice which was just great and we got to deplane through the back at both airports. On time, nice.
If your flight is during a meal time I would recommend bringing a snack, the flight is usually about 1 hour 45-50 minutes once you're up, so if you get hungry. I haven't flown UA since '99 but if I remember there is a Wolf Gang Puck's in the LAX T7 - do that! Unless you like fast food [which I don't] and you'll see your fill of Starbucks in the NW.
Yeah, PDX is kinda a cool little airport, and if you're there from around 10am - 1pm look for up to 4 DL MD-11s until March 31. In Portland go to Powell's Books on NW 10th and W Burnside. It is such a good book store. ALso 23rd street is cool and Jake's seafood is really good. Ok, sorry to be so down beat about the flights. Good luck and have fun.