Apple released the iPhone OS 3.0.1 firmware update the other day to fix an SMS security flaw. This has rendered purplera1n useless, and creator Geohot has abandoned the project for now. That being said, redsn0w from the iPhone Dev-Team still works.
There's one thing to look out for when using redsn0w to jailbreak 3.0.1. After updating to the official 3.0.1 through iTunes, running redsn0w will ask for the IPSW file to use for jailbreaking. Select the 3.0 IPSW, not the 3.0.1 version you just installed. For owners of the iPhone 3GS or a newer 3G, you may not already have this file.