I know about two Thanksgiving dinners. Fortunately, mine aren't on the same day.
I just got back from the first. It's a tradition that dates to 1982, when some college friends who had an off-campus apartment, decided to host a pot-luck Thanksgiving. That first year, I was still in the dorms, and didn't have a kitchen, so I just brought cranberry sauce in a can (yuk). We sat on the floor, the table being plywood resting on cinder blocks. We've been doing it every year since!
Whoever has the biggest house at the time offers to host, and cooks the turkey. Everyone else brings the rest. I still bring cranberry sauce, but freshly made with Cape Cod cranberries, oranges and fresh ginger (recipe is on the condiments thread here). It's always the Saturday before Thanksgiving. Nowadays, it may be the only time of the year I get to see some people. Now, there are lots of kids, straight, gay, couples, singles, (interestingly, fewer vegetarians). But the same core group of college friends--28th annual this year!
The second dinner, on Thursday, I'll cook, for a much smaller crowd.
I'm very thankful for my wonderful, loyal friends.