When you operate within the bounds of a closed system like Apple does, it's only a matter of time before some pioneering group of users come along and smash through your security. In this instance, a "matter of time" is made up of a handful of hours, because the iPad has only been out since Saturday and already a member of the cheekily-named iPhone Dev Team (who have nothing to do with the iPhone's development, par se, and everything to do with making jailbreaking as easy as pie) is claiming to have jailbroken the iPad.
Said member goes by the name of "MuscleNerd," and apparently the iPad was so quickly cracked because its security isn't much different from the iPhone, which was defeated by a browser-based hack. The benefit of jailbreaking is that you can run apps developed in an open-source environment and not approved by Apple. The downside? An update could render your iPad useless, and its harder to take advantage of improved features from updates beside.
Right now, the process is too involved for the average user, but if you give it some time it'll probably be as easy as pressing a button. You can see the jailbreak in action in the video below.