I used to dislike the idea of video on DSLR's and thought it had no business being on there. However, after seeing the capabilities of the Canon 5D MKII first hand, I've chaned my position on this.
Initially I think it was just a race between Nikon and Canon to get HD video on a DSLR. The Nikon D90 grabbed that title but to be honest, I found it more of a gimmick, than anything else. No AF, having to preset the exposure. I didn't find it very practical. The results to me didn't look that great either.
The Canon 5D MKII, is a very different beast though and produces fantastic results, bettering those of dedicated video cameras, several thousands of pounds more costly. For people who shoot both, its the all-in-one solution. I should imagine it would appeal to wedding photographers/ videographers greatly. Its a fantastic camera in its own right for taking stills with but as the technology develops still further, the video functions will become better still. I'm very much looking forward to the MKIII - and I'm a Nikonian lol.
Personally, I think video on DSLR's is now a permanent feature in virtually all DSLR's. Nikon will have lost out quite heavily to Canon in the full frame market over the 5D MKII, due to its video function and I would have thought that its long awaited D800 should rival, if not exceed the 5D's abilities. We shall have to wait and see.
In the meantime, check out these links to some amazing scenes shot on the 5D MKII
http://vimeo.com/18467488
http://www.youtube.com/watch?v=uBLccEDmn40 (remember to switch to 1080p to get the best results)