Originally Posted by
neuromancer
If you receive an invitation from a hotel program, you'll have all the airlines and only that hotel program. If you receive from an airline, you'll have only that airline and all hotel programs. If you receive from something that is not a hotel or airline (like Blockbuster or Hertz), you'll have access to any program.
An exception is British Airways, they allow access only to their program.
Thanks for your quite useful response. I guess my best bet in the short term is to use my invitation from Hilton, as I'm most interested in being able to have the ability to occasionally deposit miles into airline accounts that I'm not using much, so I don't lose miles. Airline consolidation has made managing my family's varying accounts easier, but it's still a challenge.