Waste of money. The d90 is not really considered the "consumer" dsrl anymore. Unless you're big on photography and really want to pursue it, you're just wasting money just so you can shoot video.
The big thing about the d90 is that it shoots 720p clips. Not sure if you know but you can only record up to 5 mins. So basically your putting in a extra $600~ give or take just to shoot 5 mins of 720p video. But hey, if you got the means, then why not. From a purely financial perspective, its not worth it.