I have been considering getting an AP because we are planning two trips, one in December and one at the end of April. We would normally buy a six day park hopper for one of these trips. But because we are planning two trips, I think we will save something like $228 for two annual passes over buying two six day park hoppers.
ETA:
Okay, here is the price breakdown for one adult ticket purchased on the WDW website:
annual pass with tax - $648.59 which would be an average of $216.20 per trip
one four day ticket(without park hopper) = $297.14, if you bought one for each of your three trips, it would be $891.42.
Even if you bought four day tickets for two of your trips and a one day ticket for your third trip, you would still save money by getting an annual pass.
If you normally buy park hoppers, then you would save money with an annual pass even if you only took two four day trips. since a four day park hopper costs $359.97 and two of them would be $719.94.
We always buy park hoppers. It is almost required for a stay at an Epcot resort.