No useful information - just ramblings
I don't have one on order yet, but the 5DMk2 was the camera that I was waiting for its official announcment before deciding on what to do with my underwater camera system.
Naturally, there's always second thoughts. For example, a Canon PowerShot G10 would result in a significantly smaller UW system ... and be cheaper ... but I'll have to see if it can work to do superior Wide Angle work, since it only opens up to 28mm equivalent (with my Nikonos, I've been shooting 15mm).
Given my most recent vacation trip, one of the things that I found to be a noticable issue at times with my 20D was the autofocus (telephoto & flying birds). My recollection is that the 5DMk2 didn't really receive any changes to its AF sensors, so I don't know how it might compare...
...but as such, AF performance (speed) is going to be one of the things I'll be looking for in reviews, although the comparison baseline should probably be a 40D or 50D, as I could sell one of my 20D bodies to upgrade for the crop-body based telephoto stuff. Nevertheless, the 5DMk2 is for me still is primarily as an interest point for shooting wide wide angle.
-hh