I recently purchased the Canon T4I...and I shoot Nikon D7000 and the D300. My observations from the field:
1) Canon menu system is more easily navigated than Nikon's. Touch is convenient.
2) Image quality is very good for this pro-sumer camera. 18mp is more than enough, imho.
3) I really like the built-in HDR and Handheld Night shot settings...very easy to get quality results (great for beginners).
4) When shooting night-time with Bulb setting, T4I has a built-in timer...VERY convenient - neither Nikon D7000 or D300 has that feature.
5) Light; articulating LCD; live-view; Full HD video...what's not to like?
1) 5fps (ok, maybe not a con, but both my Nikons shoot faster - 6 & 8 fps, respectively).
2) Fewer buttons than the D300 or D7000 (could be a plus depending on your perspective).
3) No secondary LCD (but I think the touch screen makes up for it, imho).
I'm sure I could come up with more pros/cons. Overall, though, I like this camera. I'm using it more and more and I'm very pleased with the results I'm getting. Would it replace my Nikons? No. But I consider the T4I a great second camera, and its ease of use makes it a great first-responder when I'm in a hurry.