redsn0w+limera1n fun
It looks like geohot’s recent limera1n exploit for iPhone3GS/iPhone4/iPad/ipt3g/ipt4g/atv2g will be very beneficial to jailbreakers and unlockers for the next few months (at least). geohot’s limera1n program and the alternative greenpois1on program both use his same exploit (although greenpois0n refuses to tell you that, FWIW), and hopefully SHAtter can be saved for some later device.
In the meantime, we’ve also incorporated the limera1n exploit into redsn0w. But we’ve added a few extras:

custom bootlogos for iPhone3G/iPhone3GS/iPod2G users (with qualifying bootroms)
an option that implements the “DFU” button in PwnageTool. This button (which you can use from Windows) lets you prepare your device for a custom DFU. Even if you’re purely a Windows user, you can get a trusted friend to run PwnageTool over your IPSW to create a custom IPSW. You can now install that custom IPSW on your own Windows box, after you run this redsn0w version.

This latest redsn0w is available at:

OS X
Windows

For Windows users who have run redsn0w and chosen “Just enter pwned DFU mode right now”, your device is now completely vulnerable. Running iTunes and selecting a custom IPSW from PwnageTool (choose it by pressing Shift+Restore)….you’ve now convinced your device and iTunes to restore to a custom firmware. Congratulations!
If you are timid about software and running these programs…please just wait! Don’t jeopardize your carrier unlock for a firmware upgrade. Wait for even easier methods than this latest redsn0w release.