Jo,

I'm pretty sure the break-even amount is 8 days for an AP.
We had 5 day hoppers which we upgraded to APs at the start of a two week trip in Dec.
We ended up saving money on that trip alone (parking, 5 nights stay at Animal Kingdom lodge, 10% off Planet Hollywood, 10% off World of Disney at DTD).
We also knew we were going back just before they expired for 3 weeks so APs made even more sense.

The only problem is that we have now decided to do a cheapie (yeah right ) end of April for 8 days because 'we have the passes so Disney will be free'....No willpower...So after saying it saves you money it has cost us an extra £1500-ish....lol

Best bit I reckon is popping in just to do one/two things, we did TestTrack and Mission:Space at Epcot, then leave. With a Parkhopper you have wasted a day, not so with an AP. We also did a couple of hours in MGM on our way back to the airport which made the last day so much better then previous visits...one last chunk of fun.

I'll post a straight cut & paste from the AP area detailing the discounts after this post.

Brizzle