Darren,
Thank goodness someone actually shooting the camera is taking time to share insights and questions as you get more comfortable with the Canon 5D MK II video capability! Versus endlessly discussing tech specs 
Being an Ikelite housing user of course something "improved" will be forthcoming (maybe in 2009 an APS-C dSLR with HD video for less $$$ perhaps?) But the 5D MK II is here NOW.
I have numerous customers who get 2,3 or more years out of their dSLR bodies then only need to upgrade the housing body when they change systems. 4 folks went from older Nikon D70s to D300 in the last couple months alone. I practice this philosophy with my Canon bodies, to. Cords, arms strobes, etc. all still work seamlessly.
I also contend Ikelite housings are fine for 99% of shooters at a much lower cost. The dome port balance issue is something that certainly isn't insurmountable. Whether it be photographer's individual techniques, a bit of counterbalancing here or there, etc.
My initial thoughts after playing with a 5D MK II ON THE SURFACE only (so I'm NOT claiming to be an expert shooting it UNDERWATER) is I would shoot a wide lens primarily. Maybe my Sigma 15mm Fisheye. Line up your shot, hit the "AF" button (right under the thumb from the handle as previously mentioned in another 5D MK II thread) in Live View mode and let DOF take care of focus while you roll scenes......
Keep us informed on your actual use of the Canon 5D K II. I'm sure we all could benefit from it as dSLR cameras wade into the HD video pool 
YMMV
dhaas
Yep, I had made a decision to stay one model behind in the 1ds series in order to manage the cost of housing upgrading, going with 2nd hand housings bodies. These cameras can all do the job.
That was until the 5d cam out of course, dazzling us (and our clients) with a new capability. For me, this is the biggest revolution since I bought my 1ds way back when. Actually it's probably a bigger revolution than that as I had already being working digitally for years, albeit via film+scanning.
Things seem to moving ahead on the housing front for sure. Jean's posted the rendering of the Aqutica solution which looks great.
Like you say lotsa people talking about the pros and cons without having one in the hand let alone getting one wet ( know what i mean). And also a lot are critical of the the video implementation, when in fact I think it is actually a perfectly good approach for us still shooters learning video, especially UW.
I think that things like no AF during recording are irrelevant to me, as I would hate the AF to track needlessly during a clip. For wide shooting, which is what I will be doing mostly, AF on, Alock, then button on will yield great results based on hyperfocal principles with wide lenses.
On occasion a manual focus gear might help a bit.
Re the housing balance... I have issues with port-up with my seacam near the surface (where I do a lot of work), as I'm sure most folks with super/mega/whatever domes do. Its not such an issue with stills, but I can see already that balance is very important for vid. Optical quality is still pretty important to me.