The D90 is good, but the cmos sensor needed for video, produces a different picture quality image that I'm still finding hard to get used too and like!
The sensor in the D90 is the same base sensor as in the D300, and it was designed for photography- video was an additional feature added in firmware, not a driving specification. The fact that it's a stock CMOS imaging sensor is apparent to anyone doing motion video, since CMOS gives you the "Jellocam" effect because the sensor is read pixel by pixel rather than all at once. The D90 essentially takes the live view image and records it, which is why you don't get to play with settings when you shoot video with it. Liveview is the feature that made video possible on the D90, and all Nikon did was to increase the frame read rate to get to video, not put some weird or different sensor in the camera. It's a stock Nikon still imaging platform and there's nothing speicial about the sensor for video. Nikon moved to CMOS in the D2x well before video was an idea for DSLRs, the CMOS look is only a little different, and not really that noticeable unless you're doing side-by-side comparisons.
It is essentially a generational update of the D2x sensor, and it's got a typical Nikon tonal response curve, with very good dynamic range compared to the venerable D2x- so I'm not sure what there is to "get used to." While I don't own an D90 or D300, I've processed raw images from them, and they don't have anything to "get used to" from my perspective, so I'd suggest you look at how you're processing the images or your lens/lenses- because I've got 13x19 prints on the walls that don't scream CMOS from both the D2x and D3x.
Increasing the read cycles on the sensor in liveview mode does not affect the still image at all (other than potentially adding a bit of thermal noise if you're doing a lot of liveview/video beforehand, as that will heat the sensor up a bit over straight still image shots.) But that should be the only real potential downside from the video stuff.
Paul