[XanTium] sent this in a few days ago, but I thought you guys would dig it. Here are the details straight from his email:

Hackers on the XBH forums managed to change DVD key and Game Region Code in the Xbox 360 ‘Key Vault’ (that stores on flashchip: console certificate(s), per-box private keys, DVD key, however NOT any code-related encryption keys).
However you should know the ‘Key Vault’ is encrypted with the per-xbox360 ‘CPU key’, so that means this hack is only possible on Hypervisor exploitable Xbox360s (kernel 4532 and 4548) for now. You will of course also have to read/flash the Xbox360 flashchip (by desoldering it and read/flash it with programmer or for example use the versatile Infectus dev chip)

You can read up on some more details here or get a login and check out the actual forum thread. The end result: play EU games on your US 360. (It doesn’t sound like the DVD movie region has been successfully changed, but modded DVD players are easy to make.)