I have the DC310 with the external strobe. I like the camera and have taken some nice pictues with it over the past few years. I have also taken lots of bad ones.
Pros - Easy to use, Travels lightly, Rugged, takes nice pics at a high enough mp that i have even blown some up to 8x10's that are hanging in our living room, uses AA Batteries (4 strobe, 2 camera) - I use the lithiums and I just returned from a 26 dive trip where I had to change batteries one time
Cons - Minimal controls while underwater (basically on and off), Maybe use error but I tend to blast lots of stuff with that strobe - I think I am going to puchase the diffuser to see if that helps, Very buoyant - can be helped with a sealife weight, slow recycle time between pictures
Overall, I think it is a good beginner camera or at least has been for me. I don't have anything to really compare it to though. I would recommned though getting the DC600 since it is newer, has more controls available underwater, larger lcd screen, quicker recycle time from what I understand, and I think it is more compact The only negative I heard about the newer ones was with the DC500 is that they use rechargable batteries that can tend to drain quickly. This may have been fixed with the 600. Maybe someone else could shed light in that area.