Mac OS X only: The iPhone Dev Team has already released the iPhone 3.0-jailbreaking Pwnage Tool for Mac OS X (just two days after the iPhone 3.0 release), with QuickPwn for Windows and OS X soon to follow. There are a few catches, though.
This current jailbreak has its peculiarities (it doesn't currently work with 2G iPod touches or the iPhone 3GS), so before you go straight to the download and jailbreak, be sure to read up on the full blog post from the Dev Team. The real question at this point: The better the iPhone 3.0 software gets (and this really is the best it's been yet), the less reason many people have to jailbreak (unlocking for other carriers is another story). Is a jailbreak still worth it to you? Let's hear your thoughts in the comments.