Canon EOS 50D
15.1 MP
ISO100 to 3200, also supports up to ISO25600 but it's simulated ISO.
6.3 pix/s (which is OK for birds in flight)
My inital test with birds-in-flight (gulls and terns) shows good tracking capability.

Some conclusions (after some 6000 frames):
I have both 40D and 50D and I've changed back t0 40D a couple of times but quite soon I change back to the 50D. It's an awesome camera to catch details but it's more difficult to use.
Compared to 40D I have found 50D to:
1) Capture more details than 40D (especially in good light). You can be further away from the bird (ie crop harder).
2) At standard NR settings the per pixel noise is worse than 40D (despite what some people say on the internet forums). 40D shows less noise (at ISO800)
3) The dynamic range is not as good as on the 40D. You get blown highlights easier on the 50D. It's not a big difference but noticable when you shoot the two cameras side by side (again some people in the discussion forums says the 50D is on level with 40D but I don't think so)
4) Maximum useful iso is ISO800, but good result can be obtain with iso1600 if you can get a good exposure and use the full frame (ie can't crop that much as with iso800)
5) Normally more post processing work is needed with the 50D images to obtain good result and without downsizing (NR and protecting bright areas from blowing out too much when doing level adjustments). After doing proper post processing you get more pixels for printing compared to 40D.

All in all I prefer the 50D over the 40D for my work (mostly low light, no flash bird photography) but the 40D is also a very good camera. My wife is using the 40D on the 500/4 lens and when comparing the pictures she also wants a 50D.