With great power comes great responsibility, and with added codec support comes a crapload of new questions. That's why Microsoft's Xbox team has released a FAQ detailing what you may or may not want to know about the newly supported codecs.
Among the more interesting answers (as if knowing what setting to choose when re-encoding content for your Xbox 360 wasn't interesting enough) is the "No." to "Do you support DivX", the "No." to whether they support MPEG-2, and the fact that you can now play back some 1080 content at 30fps. Head on over for a look.