I've been thinking about how Nikon may respond to the 500D. It seems to me like the 500D is Canon's answer to the D90, and beefed up a little in response. But I don't think the D90 is on track for a replacement this year, unless I missed something. The common rumor is the D40/60 and D300 upgrades are this year - but neither of those will respond to the 500D directly.
The D400 should definitely best it in every area - more pro body, 15MP sensor I would guess, and better video options (I should hope!). At least 24fps 1080 video with better manual controls, mic input (a must!) and possibly autofocus, though I wouldn't bet on that. Nikon generally gets pixel density right and the high ISO *should* be better than the 500D, though the 500D's ISO 12800 shots were pretty impressive - noisy, yes, but *very* detailed considering, and would clean up beautifully. But I have faith in Nikon - the D400 should have KILLER High ISO.
I don't know if they're going to put video in the D60 replacement, but even if they do, the 500D will still probably be a better camera, simply because it's the next "class" up. But if Nikon doesn't have a D90 replacement scheduled this year, I think a lot of people who are "on the fence" may go toward the 500D. I'm just wondering if this will affect Nikon's game plan at all.
Personally, I'm praying for the D400 with the specs I mentioned above. I've held on to my D80 long enough :)