Some years ago, I helped a now-former-co-worker with his moviemaking. My biggest contribution was being the caterer and making sure that his cast and crew was the best fed cast and crew in the entire bay area film scene. (And succeeded. Who else gets a wide variety of made-from-scratch goodness, with each meal being different from the last? Most of the time, it's just OJ and donuts. All day)
Anyway, one of the other things I helped out with was the depth of field adapter. See, depth of field is just as important in moviemaking as it is in photography. And so our depth of field adapter was made out of parts of an FD-mount extension tube and some Canon FD lenses. With the adapter, we projected the aerial image from the lens onto a ground glass and then shot the ground glass in the camcorder.
Anyway, the D90 is game-changing, for both video and photography. Photographers get access to HDTV video. Videographers get access to a wide variety of lenses and depth of field in a reasonably priced form factor. The APS-C sensor in the same ballpark as the side of the academy frame.
This is much cooler than you'd think at first glance. We won't see the results of it for a bit, but when the world really figures out how to take advantage of dSLR video, we're going to see some interesting stuff. Good control over depth of field is important in photography. This is why people whine about the tiny sensors in compact cameras. It's also important in good videography, but there's never been anybody who's really done much to make that accessible. The same goes for lens selection. There's tons of different lenses available for the high end movie cameras, but very few options for mid and low end video cameras.
In the early nineties, the Video Toaster provided a side door for a group of people into the video biz because their Amiga could suddenly do editing for cheap. In the late nineties, people started bringing MiniDV cameras to a shoot. At the time, it felt like bringing a knife to a gunfight, but once movies like Timecode came out, it started making more sense. This was despite the quality not quite being the same... DV isn't nearly as nice as real 35mm film. But the results were good enough to impress.
This is what the D90 and the copycat cameras that will inevitably follow promise. Not necessarily as big of a revolution as MiniDV, but there will be some new and interesting video out there.
If you want to complain about the lack of functionality... the lack of stereo audio doesn't matter that much... that's why they have a clapper board in Hollywood... so you can align the click of the clapper board on the audio to the visual point where the two pieces meet in the video. And the lack of autofocus doesn't matter, because you are probably going to want to focus it manually to take advantage of the smaller depth of field.
You should also check out Oren's site. There's a continuous stream of demented genius coming out of it