I think the 5D Mark II is a great piece of kit the high performance for stills at ISO rating are superb and is a must buy (if only I could afford it
).
For video it also is a great camera but would I use it to film a wedding or corporate event NO, not a chance, as both are about video captured as well as a professional look and filming video from an DSLR will not cut it, handling alone would right it off for both types of jobs. Give my a shoulder mounted HDV camera any day of the week.
But would I use it for wildlife or personal projects I'd say hell yes it's an ideal tool as I have the lenses already for me using it for stills, and (the big one) saves me lugging another complete camera system around if I want to do stills and video (this is usually for wildlife or personal stuff anyway).