I've used photopass on my last two trips, one to DLR one to WDW. Comparativley there aren't many locations in DLR. Also the trips tend to be half as long.
That said while I was in WDW there were very few photographers available than the PP site shows on their maps. I chalked this up to it being a slow period for the parks.
That said, to get a bulk of pictures needed to fill the book or CD the items which use the most pics and cost the most wasn't easy. Without duplicate shots, same photographer same spot, same time, I got about 25 in DLR and 80 in WDW. So about 1:3 and I was really trying hard to get a lot in WDW. The price for the CD is 60:150, DLR:WDW full price of course. But the book is the same.
IMO I would get a cd in DL and only questionably use it in WDW. The only benefit I saw was that I could easily pictures of my son and I, while my photos are all of my son.
I also should note that if you get the CD you can put the pics on your computer and upload them to several sites to make the picture products for cheaper. They just wont have the disney patterns on the backings.