Wow. Some Xbox game bashing going on here, you people must've really suffered while playing them. To me x360 games aren't yet leaps and bounds better than few quality Xbox games, so I still play the oldies. (and yes, I have a HDTV set).
You whined to MS for them to implement BC to x360 and now utilizing it is somehow a bad thing. . Surely, if you want to play boxing, snowboarding or Ghost Recon kind of game, you're much better off with the x360 versions, but there are so many genres that x360 is still missing that BC playing makes sense if you want more variety.
A few examples:
Splinter Cell CT - There's no spy-game substitute until the new SC comes out. Plus it looks ace in 720p.
Halo 2 - Still the king of online shooters
Super Monkey Ball - Again, a genre that's still missing from x360. Heaps of fun and looks good in HD.
GTA - Better than x360 freeroamers, which don't exist. Again, in 720p looks pretty much like the popular PC version and was never about gfx
Barbie Horse Adventures - Just kidding here..
I'd also include Forza, which still washes hands down PGR when it comes to game play, if it'd run with decent frame rate in BC, which it don't.
EDIT: metalhead beat me to it. well put, man.