Some more fuel for the fire of codesharing seat assignments...
1. I have booked a UA ticket containing a flight operated by US, and I did get a seat assignment at the time of booking. Interestingly enough, after checking in with UA, I had to check in with US to get the sole boarding pass for the flight operated by US.
2. I have booked a Delta ticket containing a flight operated by American Eagle, and I did get a seat assignment at the time of booking. E-tickets were not available for this type of codeshare, so I got paper tickets.
------------------
"Where's my money?" -- Pizza the Hutt