I agree 100% with NWGrateful diver - I see sooo many people with cameras who put themselves in situations that compromise their own personal safety, annoy the rest of the dive group and damage the underwater environment - and this is often regardless of certification level or experience.
Last week I had an underwater argument with a diver from another centre who was quite clearly an experienced diver, but had terrible control when he was using his camera. He was either kicking the coral or lying in it, so far behind his group that he was effectively solo diving, at a reef which can turn treacherous if the current picks up. When he was swimming along with the camera he was fine, but when he stopped to take a photo, he was all over the place.
After seeing them in the water with the camera on the first dive, I have asked customers to leave their camera on the boat for the next dive - in fact probably all of my colleagues have done so at some point, and we are well supported by the management in refusing to allow them to dive if they bring the camera. In many cases - wow - buoyancy control, buddy separation, air consumption and basic dive protocol improve immediately and dramatically without the camera.
Some examples I see: People who are low on air and making a safety stop will suddenly bolt back down to 20 metres to take that all important photo of the turtle swimming by, or swim as fast as possible to chase the shark that is so desperately trying to get away from the underwater paparazzi, abandon their buddy and in fact the entire dive team to get the perfect clownfish photo, rest their camera on top of a table corals as if it was some sort of tripod, or run out of air after 20 minutes on a shallow dive because they are so focused on taking pictures of what often turns out to be blue fish swimming away from them against a blue coral background in a blue sea. When the photo becomes more important than the dive, the camera becomes a liability, not an asset.
However - with some basic training, and some understanding that taking photos underwater can seriously annoy a lot of other people, taking out a camera for some point-and-shoot fun is fine. If competent photographers are willing to abide by the safety rules of the dive, I will go out of my way to make sure I take them to the best things that can be photographed and I generally, as a dive guide, swim slightly slower than a snail that just took a toke on Bob Marley's finest.
In general, I'm happy to accommodate photographers as long as it is not to the detriment of the rest of the group in terms of safety and enjoyment. I love it when my customers send me the pics afterwards, because actually I don't have a lot of photos or movies of me diving, so I rely on them for my scrapbook. BUT - if they hurt the coral, annoy the group or compromise safety then they can dive without a camera, or they can't dive at all. Very simple.
In my opinion, the best cameras for the non-professional photographer are the Canon Powershot series, with associated underwater housings, which will give the inexperienced photographer a lot of leeway with the mistakes they will make, and have all the manual settings required to make more competent photographers happy with their output without having to invest in a DLSR + Housing. Somebody mentioned the old big yellow Sea&Sea jobbies - er - no, they suck, sorry, even if you know what you're doing.
If you can bring a camera and not lose sight of the overall objective of the dive, go ahead, but if you find it compromises your actual ability to dive, consider the situation in which you are diving, and whether or not it's acceptable to the team.
Cheers
C.