Originally Posted by
spartan3186
If you signed up via an airline, you'll see all hotel partners, but only the airline you signed up with.
Weirdly, that isn't always true. I signed up through an airline, and have always had the option of depositing miles with other airlines. Maybe I'm just lucky.
EDIT: Actually, what beachmouse said above may apply to me--I think I signed up under Continental just before the merger with United was complete. I always had everything, so I think it was just very, very good timing!