Just today, I boarded a WestJet flight(WJ34) from YEG to YQU(Grande Prairie), so now I'm at my family's place in Grande Prairie for the weekend. But one problem existed. I saw a lady sitting in the seat I was supposed to be assigned to - a window seat about halfway down the cabin of a 737-200. With her child and husband. I spoke to the FA, and they kindly told me to wait in the back end of the cabin until nearly all the passengers were seated. One FA even told me no, it's OK, but the seat was still occupied! So I asked the lady sitting in my seat what her seating assignment was. She politely showed me and it was exactly the same as mine!!!! I told the FA "we've got a problem" and to see if she could get me another window seat, as I didn't want to have to separate the family. Luckily they found me another window seat even though the load factor on that flight was quite high - at least 90 out of 112 seats were occupied. I figured there must have been a goof-up by the counter agent. A WestJet passenger is given a confirmation number and only when the passenger arrives at the airport check-in does he or she get a seat assignment. So it's probably not that uncommon. The FAs have been very nice throughout the whole flight, and what a nice flight it was!
I had a very similar problem on a CRJ flight from YYZ to YUL, but it was because of an equipment change from a 767-200! I've experienced seat assignment goof-ups on CRA Dash 8 flights, too, but only once or twice.
Has anyone experienced problems with seating assignments before for whatever reason? (I did see one thread posted by RedAirForce under my topic "Air Travel In Russia" that Russian passengers ignore seating assignments, sitting wherever they please on flights within Russia!)