We have published a tutorial on using this jailbreak method. You can find it here
Yes, this is what you've all been waiting for. A jailbreak for the iPhone 3GS. And it's awesome. To get started right now, go to purplera1n.com. Download it. Make sure you have windows(but not 7), the latest iTunes installed, and an iPhone 3GS with 3.0 firmware. Connect your iPhone normally. Click "make it ra1n". Wait. On bootup, run Freeze, the purplera1n installer app. Hopefully you'll figure out what to do from there. Best tutorial gets linked to from purplera1n site. This tool is beta. Make sure to have everything backed up before running. Also if Cydia doesn't show up after running Freeze, reboot.
If you need help email purplera1n.support at gmail and attach your purplera1n.log file. Or call the purplera1n support hotline @ (650) 265-1210 Mac version is coming shortly.
Normally I don't make tools for the general public, and rather wait for the dev team to do it. But guys, whats up with waiting until 3.1? That isn't how the game is played. We release, Apple fixes, we find new holes. It isn't worth waiting because you might have the "last" hole in the iPhone. What last hole...this isn't golf. I'll find a new one next week. Also your purplera1nyday files ensure that you can always get back to a jailbroken state, so if you have it it's just a matter of tools.
Props to chronic dev for their help, and to kroo for writing v2 of Freeze. And props to Saurik for making an awesome package set. Note the binary size of purplera1n, it's smaller than C++ hello world. No 20MB thing that needs to be torrented. And no IPSW to download. This is how jailbreak should be!