Last night, I jailbroke my iPod Touch 4G (iOS 4.1). Now I have the best of both world on this thing. I can run Apple approved apps, as well as unapproved. I use Cydia
as an unofficial App Store, and I love it. I installed a Windows 7 Theme onto it. Now that jailbreaking is a protected right in the United States, I'm very happy. So far, I've yet to see any drawbacks to this jailbreak other than a void warranty. (I've never had to use a warranty before anyway). I'm hoping to somehow get Flash Player onto this thing now.
The jailbreak is not tethered. Rebooting the device does not undo anything. Props to the hackers who made this possible. It rocks.