Except for most it's useless...
According to what I have read, for most it is all but useless. You need to be able to boot a homebrew app to extract some keys from the console, but the homebrew was blocked with the Summer 09 update, so unless you happened to get your keys before doing this update then you're screwed.
Plus it means the donor console can't be used online again.
Too much trouble if you ask me. Might as well go out and buy a new console and the games.
Personally I'm happy playing some of the older releases which have been out a while and been reduced in price. I dare say I'll be trying MW2 when the next XBOX is released :-)
Rob (who hasn't modded his XBOX 360, but doesn't play on Live either).