My goodness, the biggest problem with the video mode in the 5D is that it is set to auto exposure and everything. That means that you can’t even set the F/stops and that plus the fact there is no useful autofocus makes it pretty useless unless you have still subjects. Now version 1.1.0 at Canon fixes this by allowing manual exposure control so you can set in manual mode the shutter speed, the aperture and the ISO. So you don’t have aperture priority, etc., but at least the thing can’t go crazy on you.
Also claims to fix some problems with the Auto Light Optimizer interacting with highlight tone priority. No idea what that is.
There is also some hackers out there on cinema5d.com who are working on things like audio meters for the video system. Basically, the hardware is sort of there with the 5D, but it is far from a camcorder replacement without autofocus for instance or someway to control the audio.