Mr. MuscleNerd himself, has just posted a screenshot from a jailbroken iPhone 4. Before you get too excited, however, you should know that this is just a preliminary "userland" jailbreak, which means it uses Apple software to happen, and it's not of a low enough level to really be worth releasing, since it's easy for Apple to patch. Instead it's an important step toward a real, low-level jailbreak that can actually be released. We'd feign pins and needles if this community wasn't so gosh darned amazing at hacking these phones: we're sure that real jailbreak will be along shortly.
[Thanks to everyone who sent this in]