The Froyo (Android 2.2) update for the Evo 4G has been rooted. While the current method is a bit hairy and involves timing and a bit of luck, the directions look very straightforward, and more important, not too dangerous to your precious hardware. The method is a mix of the recent exploit used on the Droid 2 and tools from the UnrEVOked team, and should leave you with a fully rooted and bootloader unlocked Evo, ready for your choice of a custom ROM.
Remember, this sort of thing breaks warranties and has the potential to ruin things, even if this method looks fairly safe. Proceed at your own risk, or wait it out a few days to see if an easier method rolls around -- nobody here will blame you. But you trailblazers, hit the source link to give it a go! [xda-developers] Thanks Chuck!