I get the prepaid CD and I find it to be a great deal, however many photos we get, and it is usually a lot because we are never rushed in the parks. Whenever we find a Photopass photog we stop and let him do his thing, and it usually amounts to 2, 3, or 4 photos per stopand then when we get home we log on to the photopass website and edit them all to add borders etc. so we end up with at least two or three times the original amount of photos taken. All for the prepaid price.
I imagine they can get some pretty fun shots if you're not as rushed as the typical WDW guest!