You can re-use redsn0w v0.8 we released a few weeks ago to jailbreak today’s 3.0.1 update. Just let iTunes update or restore you to official 3.0.1 then run redsn0w. The only “trick” is that when redsn0w asks you to identify the IPSW used, point it at the 3.0 IPSW instead of the 3.0.1 one. After the jailbreak, reinstall ultrasn0w 0.9 if you need the unlock. The 3.0.1 release is a “branch” from 3.0 that occurs (code-wise) before all the 3.1 betas. The programs redsn0w needs to change for the jailbreak are identical when you compare the 3.0 and 3.0.1 versions. It seems pretty much the only changes Apple made were for the SMS bug, which affects programs that redsn0w doesn’t touch. That’s why you can re-use redsn0w 0.8 on 3.0.1 even though it was written for 3.0. And since 3.0.1 doesn’t touch the baseband either, ultrasn0w 0.9 works for those needing the soft unlock. Just install it from the repo666.ultrasn0w.com repository using Cydia as usual.

• iPhone OS 3.0.1 security update out, fixes SMS security vulnerability issue
• New updates for Ultrasn0w and reds0w now available
  

Via iPhone DevTeam Blog