I have a D90. It is not usable as a motion picture camera at all. You need to evaluate if you're buying a motion camera, or a still camera. The D90 is a fantastic still camera...but if you're just getting into photo and don't have an investment in lenses...get the 5D.
I believe there as an update to the video processing on the D90 which removes a good amount of the jello-cam that blhack demonstrated. Although as an HD video camera, the D90 is still a little lacking (no 1080). As a stills camera, it is excellent.
Disclaimer: I use Nikon cameras (though not for video).
I have the D90 and have played the Canon. The D90 is no where near the same page for quality. It only does 720p for one and second it has a "jelly" motion issue where the sensor is not fast enough and if you move while shooting it gives a weird effect. Also you can only shoot five minutes at a time then the sensor needs to cool down.
If you don't pan at all, and use AE/AF lock effectively, you can shoot some decent 720p shots of static objects. Otherwise, fuggedaboutit. I shot about 3 clips with mine before giving up. I bought it for still shots, but this Canon makes me a bit envious.
