How much is video important to you?
I don't think the Nikon D90 autofocuses during video and it only goes to 720P? (I just can't remember. It's been so long since I looked at that camera.)
I've got the Nikon D5100 and am ecstatic with the pictures that I get out of it. But I don't do video. I've had the camera for 5 months?, which replaced my Nikon D70s and I use it along side my old Pentax K100d. Within that 5 months I've fired the shutter about 8,000 times but only taken 2 video clips. And once it was because I accidentally pressed the record button while experimenting with live view. <grin> Yeah. I don't do video, or windows for that matter. But that one time I used it, I think it did do autofocus during video and goes to 1080P.
The Canon EOS 550D I've read that it has autofocus disabled by default,
Digital Photography Review mentioned this in their review.
And
Digital Photography Review mentions that the Nikon you can't change aperture while shooting video. Instead you either have to stop or take a picture for it to change? Not sure what to think of this because I don't do video so I've got no opinion on if this is really that much of a down side.
Just some limited tidbits on things I've read.
But my curiousity has been peaking on this dSLR Video thing and I'm going to try out my buddies new Canon 7D today when I go to his house and try out the bells and whistles on his camera.