The illustri-notorious Dev Team has blogged about Jailbreaking iPhone OS 2.2.1, released by Apple earlier this week.
Simple version: You can now Jailbreak, if you haven't already upgraded to 2.2.1 via iTunes, are using a Mac, aren't affected by the OS X 10.6 DFU-mode bug, and -- if you want to keep using yellowSn0w for unlock -- are happy to spin your own custom firmware.
Complex version: involves closing the barn door -- see here.
(For community-based jailbreaking advice and support, please check out our Jailbreak Central Forum)