True, I guess it means they could ditch their AT&T contracts and switch to another carrier (most likely T-Mobile in the United States). But that's not necessarily an improvement, especially when you consider the fact that you're losing certain functionalities of the device, such as visual voice mail. And guess what, the iPhone is still restricted to the same EDGE network on T-Mobile as it is on AT&T. It is restricted to EDGE no matter what network it is used with.
Detaching it from the AT&T network is one thing. But total software control is another. Apple misstepped when it made the iPhone such a closed system. While I can see Steve Jobs' point of view (that he wanted users to have a stable experience and third-party applications could cause potential issues for the iPhone), I don't think it is an entirely valid argument. Sure, there is a lot of potential for some cool iPhone applications. We've already seen some interesting workarounds via the browser. I trust Apple to develop good applications itself, however, and pass them down to the iPhone when they are ready.
Another thing to consider: Are there really that many people waiting to buy an iPhone that is unlocked, free of AT&T's network and free to be modded and hacked? How much is it going to cost? Will the unlocking software (which assuredly has value) be available for free or will people have to pay for it? AT&T legal has already contacted several of the groups that have claimed to unlock the iPhone. What legal pitfalls will people be treading, and do they even care about them?
Since none of the groups that have unlocked the iPhone have made the software widely available yet, they have to care at least a little bit.
In the end, I think unlocked iPhones will only satisfy a small minority of users.