George Hotz (Aka GeoHot) recently jailbroke the iPad and now managed to jailbreak iPhone OS 4 beta 1. He posts a picture via twitter showing blackra1n and Cydia installed.

Also, a few days ago, the Dev Team and MuscleNerd posted a video of iPhone OS 4 beta 1 jailbroken. No ETA, however, it is hoped that GeoHot waits until the final iPhone OS 4.0.