Despite the flexibility in your travel plans, I might reconsider whether it would be all that great a value if the airlines you fly do not include Northwest, Continental, Alaska or Delta. Security lines in the US tend to be longer and less efficient than in other countries and in many airports it is difficult to move from the sector operated by one airline to another. For example, at SFO UA, AA and Midwest Express share one terminal and pretty much everyone else shares another terminal, a similar situation in LAX. Is it worth it to spend the money just to access clubs in IAH and ATL, especially if you are not connecting? Anyway...have a great trip!