I'm sure most know about this, but in case you don't, there is an online magazine named Underwater Photography Magazine out of the UK. It is free but you have to register with an email address (more spam!) and then you can download the magazine in a PDF file. I think there are now 27 (or so) issues. The latest one, March, 2006, has an interesting article on using PnS cameras -- giving some good tips.
Underwater Photography Magazine