I have a pair of D200's and have played around with the D90 for a bit
also. The D90 obviously gives you a little better resolution but it's
not all that different in real world use. It also goes maybe a stop
better sensitivity for the same noise. I.e., you'll probably get the
same amount of noise with the D90 at ISO1600 as the D200 at ISO800.

But the D200 has better build, better weather sealing, seems to be the
more responsive and faster in use and is a more "pro" oriented body as
opposed to the "pro-sumer" D90

If battery life is important to you, the D90 has that hands down. It
also has the bigger screen, live view, movie mode... I.e., lot's of
bells and whistles.

If you have a D700, I think you might be happier with the D200 over
the D90. But I also don't think you can go wrong with either choice.

I'm sorry to say that it's really a toss-up, a matter of personal
preference, and only you can decide which body is for you because only
you know what's important to you... Better image quality, LCD screen,
battery life, and bells and whistles of the D90 vs. more solid build,
speed and more pro oriented functionality of the D200.