Fabulous stuff, Jeremy.
Thank you ... I owe a lot to the community at www.wetpixel.com
... they've taught me almost everything I know about shooting underwater.
The P&S may turn out to be better for this than the D700. The D700 may give you depth of field problems, though at ISO 6400 it should be okay -- especially with the help of Noiseware or something similar.
A lot of truth there ... for macro, the P&S's can give the big guns a real run for their money ... putting shutter lag aside ...
Check out this guy's stuff: http://www.flickr.com/photos/eddman/
... and this guy's .... http://www.flickr.com/photos/brianmayes/
... they both shoot G series ... and I believe Brian only uses the internal flash ...
For real w/a stuff, fisheye lenses and DSLR's really shine. It is hard to get a wide enough FOV and sharp corners with the best P&S cameras.
To shoot macro with a FF DSLR, one needs to bring BIG strobes down so you can shoot at base ISO and f22 and above. Most people stick to base ISO and rarely do folks shoot above ISO 400-800. The D700 may change that, but to date, most people say you don't need beyond ISO 800 underwater because you usually bring your own light.
That said, I'm convinced that someone will show the way and high ISO underwater photography is ripe for experimentation.
Ideally, I'd have a D700 setup as well as G10.
I'm going to St. Croix in June and don't have a camera ... I may borrow one ... or something ... as I sold the G9 earlier this year ...