I too was after an S80, but the one store that I found that said they had one turned out to be backordered. Unfortunately, I already had all of the accessories, but not enough time before my Cancun/Cozumel vacation last week to order something else. Luckily, I was able to borrow a friend's Sony CyberShot P93 for the trip so that we at least had something.
That was my first time taking underwater pics, and I definitely agree with the comment about spending the bucks on a strobe. Unless you can get really close to the subject for the built-in flash to hit it, you get a blue/bland image that doesn't come close to justifying the actual color of what you saw.
Now that I have received a refund for the imaginary S80 that I ordered, I'm looking to get something that I can grow into. I was originally impressed by the A640, but lack of image stabilization seems to be a big concern for many users. The A710 would seem like the logical other option, but the lower megapixels is where it sounds like it is falling short. If the G7 is where I need to be, then I'll save the extra cash and buy that on in a while, but is it really going to make that much of a difference over the 640 or 710? The price difference is significant, so I'm wondering if the quality of the u/w pics would also reflect the additional cost.