B&H Photo sends out an electronic newsletter now and again, and the latest issue has a hands-on with the Nikon D90 written by Allan Weitz.
It's worth checking out if only to see the sample video they have there (some nice shots; though watch the curve of the helicopter blades!) I don't think it says anything particularly unexpected about the feature:
[...] the camera's DX-format CMOS sensor is far larger than the sensors found in most consumer camcorders. As a result, the image quality of video captured with the Nikon D90 is noticeably sharper and contains fuller detail and tonality in the mid-tones as well as in highlights and shadow areas.
[...]autofocus and viewing the action through the camera's viewfinder, is replaced with viewing, composing and auto focusing on the 3" display and AF locks at the moment the record button is pressed in D-Movie mode.
There's also a good explanation of the cause of the "jelly" video effect
[...]Unlike traditional camcorders that utilize global shutters and record the video data onto CCD sensors, the D90 relies on a rolling shutter and a CMOS sensor, which because it records a 24p (progressive) f/p/s frame rate in a piecemeal fashion from top to bottom across the sensor, can occasionally display image 'wobble' when recording certain types of movements.
Despite this problem, the reviewer concludes that this is a small price to pay for having the ability to call up such a cool feature at the hit of a switch, and I have to agree. If I appear to have dismissed the video capability of the D90, it's primarily because I don't already have any Nikon lenses. If I did, I'd probably be very excited about it; though maybe disappointed that the D700 doesn't have a similar feature.