Mark of markandjo.com/markblog demonstrates how to boot OS X from an external hard drive without ever opening up the AppleTV. This is exactly what Leo Laporte said (if you listen to his podcasts you will remember him talking about this, twit.tv) All of the AppleTV hacks will move to going onto an external hard drive so that you can boot from that drive and have all your hacks or you can boot from the internal drive to have the AppleTV.
Here is the video and if you want more info on the hack you can check that out here at 0xfeedbeef.com.
[via TechEBlog]