We did the Photopass on our recent trip and it was great, just as the above posters described, awesome pictures and in alot of the pictures they add things, they can make it look like you are holding Tink or Baby Simba, in one pic we have Stitch popping out of the ground right in front of us, quality of pics is great, we bought the CD too.
Above poster is right, the photo pass photographers are all over, not just at the front of the park, I got a great pic of DH and DS in front of Tower of Terror right after they got done riding. DS got pictures of him with all the Power Rangers, he loved it.
I think buying the CD is well worth it if you have alot of pictures on there, we had about 50, but you need to make sure you can get to one of the 3 places that can make the CD for you, fairly close to the end of your trip. You don't want to buy the CD and then end up having more photos taken, I don't think they could add them on.
The 3 places to buy the CD is at Epcot Photo Center, Toon Town and the Grand Floridian. We ended up making a quick last minute trip to Epcot on our last night to get the CD, thank goodness they had EMH at Epcot that night, our plane left early the next day. So double check the times of Photo Place at the GF if you won't be able to get back to one of the parks on your last day.