Hi Mobunny. I have one Canon Powershot Ixus S500 (5mp) in their WP-DC800 housing. Good to 130 feet. Had much better reviews than the larger S45/50 series, and out of the housing is a really compact camera that never leaves my pocket. If the S70 is the same series as the S50 I'd look into it carefully before you part with your cash.

The other cameras I have are two 5mp Casio Exilim ZX55's, in their own housing (forget the designation, but also good to 130 feet). The same frontal area as the S500 but about half the thickness. I haven't looked up any reviews of them, but a guest had one here a couple of months ago and was getting really good results from it. It has both an exceptionally long battery life AND an enormous on-board display screen that virtually covers the entire back of the camera - making it ideal for use underwater. I'm expecting it to be very popular.

The results one gets with 4mp cameras are often indistinguishable from those with 5mp. And under some adverse conditions 5mp is inferior to 4mp. This is certainly true in poor light conditions, such as you may well experience underwater. Look up some of the technical reviews and you'll see what I mean. I have no idea what results you'll get from 7mp, though I do know you'll need a large memory card - 1 or 2 gig.

What5ever camera you decide on it's unlikely to come with a soft case (for use above water!), but this is essential here with the salty, sandy atmosphere. I recommend you get a snug-fitting leather case with a zip closure (rather than a flap secured with velcro). That way you'll stand the best chance of keeping your expensive investment in good order. Just because the manufacturers cut corners in not including this case don't assume you don't need it - it's vital.

Still, whatever you decide on I'll be interested to see how it performs. I look forward to your visit in August!