Well that didn't take long! iOS 4.3 beta was just released late yesterday, and already there's an unofficial PwnageTool release that will let you jailbreak to your heart's content. Pretty soon the jailbreak's going to happen before the firmware release.
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For a complete how to guide, head on over to Redmond Pie. And as always, proceed with caution—jailbreaking's great and all, but maybe not worth bricking your phone. [Redmond Pie]