The T1i battled with the D5000. The T2i uses the 7D sensor which is still in the T3i. It's one hell of a sensor which is why the D7000 and D5100 were introduced and even then the 18MP Canon sensor is still damn good.
Honestly, even enthusiasts like me can't say I'd be disappointed if I went Nikon instead. If you have some SPECIFIC need like the need for a Nikon 200-400mm lens, then sure, maybe this is the right solution.
I always heralded Canon for having 5x 70-200 solutions. The two F4 lenses and now the three f/2.8 lenses. That's a huge selection, but at the end of the day the f4 lenses only gives me a mediocre step up from my 55-250 EF-S lens. While that's an option, I KNOW I will always eye the f/2.8 white lenses. Sure Nikon might not have an intermediate step, but given that my end goal is the 70-200 f/2.8 lens, do I really lose out by not having two cheaper lenses on Nikon's lineup? Probably not.
You can't go wrong with either. For me it's more important that my friends shoot Canon because we can interchange lenses. My 7D setup with back button AF makes it easy that my 40D friend can pick it up anyday and start shooting. That and we can trade off lenses and flashes.
TBH ISO6400 is gonna suck on any APS-C camera. The 5D2 can churn out respectable ISO6400 quality but it's not something you want to use day to day if you can get away with it.
I took a screenshot of the D7000 vs 7D vs 60D vs Sony A55 from Dpreview. You can use their compare-tool to see:
http://cl.ly/110S0g1M032s1w2W2l2D