PhotoPass is great -- and if you're going to be there more than a few days, the CD is well worth the cost (you'll probably spend more on soda pop while you're there)-- it's about the best souvenir and memory aid you can get. You will get all the original photos that they think turned out okay (we had a photog try a night shot that didn't get included, am sure it was too dark and blurry). Most of them will be great shots, especially if you cooperate and ham it up!
The photogs will be in several key locations -- just look for people in costume with a large camera. You can get a new card (free) from any of them -- after you have a card, you just hand the card to them before you pose. Be sure to get it back! You can also combine cards, if you end up with more than one -- write down the numbers of them on something you will not lose -- then you can still get the CD and get to your site online if you lose a card.
They will take individual and group shots for you if you ask, or just pose that way, taking turns -- it's a treat for me to actually be in some of our photos now --since I've always been the family photographer.
If you do a pose with Simba (AK), Tinkerbell (MK) or Stitch (MGM) those photos will be on the CD (you can ask if/where they do that -- it usually involves holding your hands out) -- they're really cute.
The photogs will be in front of the parks with characters sometimes, at "vista" locations near the entrance -- and at character stops. They will not be with all the characters, even in the group character areas. They do not do ride photos, and the photos taken at the Water Parks and rides (i.e. Splash Mountain) are not included on the CD (at least so far, but the system keeps being improved).
They, or a CM will also take a photo with your camera (but their photo will probably be better).
The photos on the CD are high resolution so you can get nice enlargements, and/or do your own enhancements at home. Okay, here's the sneaky tip -- you can add the enhancements to your online photos and use print screen and cropping to get low-res versions of them that are okay for scrapbooking, etc. -- but, by all means, if you're there a few days or more, get a lot of PhotoPass pics taken and buy the CD.
Don't wait 'til the last minute to go get the CD; they are available now at each park -- even if you get a couple done after you get the CD -- that you'll only have online, you'll still be assured of having gotten the CD in time (the lines will be short to nonexistent in the afternoon).
And, no, I have no "interest" in pushing the PhotoPass system -- I just really love it a lot! If you are a photographer, and there's no line, it's fun to talk with the photogs, also -- sometimes I even take their picture!