Generally, you either sign up for a specific hotel program and get only that hotel program plus all the transportation (airline/rental car) options, or sign up with a specific transportation option and get only that transportation option plus all the airline options. The people who have all possible options are the ones who signed up with a program that no longer participates with e-rewards, most notably the folks who came in via a Northwest or Delta sign up link.

Different programs have different redemption time allowance ranging from once per quarter like Hertz to unlimited like IHG or Accor. I haven't hit a cap in the number of unique programs per 30 days, and I've probably done five different programs in a month when the surveys were unlimited this summer.