Let's go over the basics. The cameras, with 18-55mm image stabilizer lenses, have MSRPs within $50 of each other, the Nikon at $850 and the Canon at $900. Spec-wise, that extra $50 goes a long way:
• Nikon has a 12.3-megapixel CMOS, while the Canon has a 15.1 megapixel CMOS.
• The Canon's 3" LCD screen has 920,000 dots; Nikon's 2.7" LCD only has 230,000 dots, but it gets bonus points for the "vari-angle" adjustable mount.
• HD video shooting is the selling point for both, but while the Nikon can handle 720p, the Canon can shoot up to 12 minutes per burst of full 1080p high-def video (though at a minimal 20 frames per second). Both have HDMI outputs, to prove how dedicated they are to high-def video.
• ISO wise, they're pretty evenly matched, from 100 to 3200, with a Hi ISO bump at 6400. (The Canon has an additional ISO 12800 high setting.) The key here is which one is noisier at the higher levels; I have my guesses, but we'll just have to see.
• Getting deeper into camera-nerd territory, the Nikon has an 11-point autofocus, compared to Canon's 9-point AF. They both boast the usual proprietary engines, for Canon the DIGIC 4 imaging processor, and for Nikon, the "exclusive" EXPEED image processing system. And obviously, both can be fitted with a huge number of lenses from their specific manufacturer, lens compatibility usually being the deciding factor for people who already have huge glass investment.
What does it all mean? I have no doubt that both cameras are worthy sons of bitches, and like their predecessors, many of their idiosyncratic ticks—visual menus vs lists, etc.—are well known and documents. Some conclusions are already in sight, given the fact that the D5000 is a direct descendant of the D90, whereas the T1i comes straight from the 5D Mk II's loins, both heavily reviewed already.
Still, over the next day, I'll be shooting hundreds of photos in different lighting conditions, in order to make sense of this two-headed temptation. Here's some further reading While U Wait: