Apple recently filed a claim at the patent office that said that it is illegal to jailbreak your iThing:
They haven't offered a reason, but considering the pressure both from the App Store developers whose apps are being cracked and distributed to jailbroken iThings and AT&T who probably doesn't like the whole 'unlock' situation, it's pretty easy to guess why they're doing this. The thing is, it's like arguing that Bittorent is wrong because you can pirate stuff over it. Jailbreaking is simply a tool that can be used for both good and evil.
Fortunately, it seems that the general consensus from the Mac community is that it would be next to impossible for Apple to begin taking legal action against the jailbreakers. First, they're all working anonymously, and second, they're just distributing code that modifies Apple's firmware. So Apple can't nail them for redistributing Apple-only firmware. Also, it seems that Apple doesn't really want to pursue the issue, but needs to make some sort of gesture of goodwill to AT&T and the App Store devs.
Here's hoping no one decides that this insane course of action should actually be followed.