Nikon has the best kitlens of all time: (18-105 VR)
Overall, nikon seems to be legendary with it's metering system
Nikon's 50 point AF beats the 50D by a large margin
Canon has a higher resolution sensor and pretty much the same noise performance.
Also, the D90 is a very capable camera. It's more portable than the D90, but offering the same imagequality. You'll miss out on the 50 point AF system though, and have to make due with "only" 11.
Well that was true before the 7D and the new 18-135mm IS and 15-85mm IS lenses were announced. Obviously, we've yet to see about the quality of all that but I'd think the 18-135mm will come very close to the Nikon 18-105mm.
Apart from that, you're comparing oranges to apples if you compare the D300 AF (51points) to the 50D AF (9Points). If you really have to compare, do it 50D vs. D90 and 7D vs. D300 since those cameras are roughly the same price.
Now that's not to say I wouldn't recommend a Nikon camera.. I think both manufacturers will offer great image quality and a good lens lineup. I agree that Nikons pro lenses have currently the edge (14-24mm, 24-70mm, 70-200mm II), but ALL of them are much more expensive than the canon equivalents (which are very good too). For me it's a case of being able to afford pro-grade lenses in the first place - and with Canon, I can. With Nikon, I probably couldn't.
And it's a very similar case with the high quality APS-C lenses: the Canon 17-55mm f/2.8 IS is expensive but unmatched in quality. Nikon's equivalent is the 17-55mm f/2.8, which costs even more and doesn't have IS. Same story with the wide angle stuff: Canon's 10-22mm is better where it matters (at 10mm) and, again, cheaper.
So in my opinion, Nikon will have the edge if money is no object and you want to go for pro grade lenses. On the other hand, I think Canon offers better bang for the buck in their highend APS-C lenses. We'll have to see how the new midrange stuff from canon stacks up to the Nikon 18-105mm. If they match, it's gonna be a draw in that segment as far as I can work out.