You will hear many responses, but let me make one point very clear. If you are using an HDSLR for video, your primary concern will be your ability to focus or autofocus. If we are using a true SLR - i.e. a camera with a reflex mirror, you will either need a loupe attachment or an attached LCD.
Here's the kicker - the 5DII, darling of the indie movie crowd, with the largest, highest res sensor in this class, only provides SD video output while recording. Dear Lord, let me tell you, nailing focus on a 105mm at f/2 at 4 feet with a slide will drive you nuts.
I had a marking wheel. I had Magic Lantern and peaking. I had an external HD LCD. I could not see what I was doing. I did not have what I needed there: a 2nd pair of hands.
Oh, you saw House M.D. with really cool close up focus tricks? That was done with a marking wheel and consistent focusing cinema primes, and a 2nd AC whose job it is just to hit the marks on cue. Alternatively, it was a locked down shot with a lot of lighting, a decent f/stop for depth of field, and little or no focus adjustment or movement. In this respect, the added DOF of a 7D and its ability to output HD video makes it a much easier camera to control.
SO: Much of this will depend on the style or intent of the video. Autofocus may be acceptable for ENG or documentary work. It probably will not be for dramatic work. You need to be clearer about what you want to do.
You may be better off with a mirrorless camera - I love shooting with my GH1, far more than my 5DII - except for the crop factor. We all love the output of the 5DII, its 1080p with full frame, but it handles like a schoolbus at Nürburgring. Additionally, these cameras are typically better for video auto focus, but that is changing. Still, the NEX series is a real price performance killer for many video and photo uses.
Most other issues are of less consequence. If the video quality matches your expectations, don't worry. Go to Vimeo to find some raw footage samples. Don't expect to edit video like your photos though. Footage from these things is more like medium quality low res JPG than full RAW.
One thing I would tell you to completely ignore is audio. Many make a big deal about manual audio levels and recording fidelity. If sound matters at all, use 2nd system audio; on board sound should be used for video+audio sync and nothing more. Seriously - a $200 recorder will do better than any camera not using XLR jack input. If you're doing drama, you need to mic the actors and/or have booms anyway - and you don't run those lines into the camera.
If you refine the question, I might be able to point out a specific issue to watch out for or recommend a camera.
Finally - no matter what you do, learn how to light (and gel) for consistent color grading. I cannot stress that enough.
