The elimination of the PC sync port, and the addition of a boatload of scene modes, plus the switch to SD card memory, and the new, smaller body size, and the new battery and battery grip mean that the new 60D is not really a "member" of the old lineup of XXD cameras that came before...this is now a camera aimed a bit above the T2i, but below the 7D. The new 60D has a swing-out LCD screen, and improved video capture...it's aimed right at the high end of the consumer market...
I think it is going to sell pretty well. The 60D's main competition will be similarly-priced Nikon and Sony cameras, like the D90's follow-up camera,and whichever multitudinous Sony models are flooding the market. Sony has a passel of lower-priced s-slr models, so many that people can hardly keep track of them.
The chassis material will be totally irrelevant to most buyers...plastic, aluminum, magnesium...it doesn't matter to the buyers who are hanging 7-ounce to 1-pound lenses off the front of $549 to $1,000 cameras. The chassis material is mainly a bragging rights thing for consumers, and a way that manufacturer's can keep profits higher and keep costs lower for consumers who are,for the most part, going to be treating their cameras respectfully. I think the 60D will sell pretty well in its intended segment of the market, unless Sony or Nikon come up with something that's super-compelling and price it very similarly. Now, if the Sony and or Nikon competitor models really blow...Canon might have a runaway sales hit on its hands.