For a few years, I was totally ignoring the TripRewards program because I couldn't earn anything worthwhile there. Then for an upcoming personal trip to a small resort town, I couldn't find any better hotel with high-speed internet access at a decent all-in price and with decent TripAdvisor reviews except a Super 8. At the time I booked it two months ago, United was an earning possiblity but AA wasn't. I just checked again the other day, and now I'm able to specify my AAdvantage account as my earning preference (2 miles/$, which is competitive with Priority Club's midscale properties, and several other chains).

It's documented at:

http://www.triprewards.com/earn/airlines/

Warning: When booking at a TripRewards-related website, do not accept any offers for Travelers Advantage, Shoppers Advantage, etc. These are programs that many consider rip-offs (do a web search), or at best are lousy deals compared to other resources FTers know about and may be hard to cancel. Just decline any chats you're invited to, because that's what those chats will be about!