iPhone Dev-Team member MuscleNerd revealed this afternoon that he has already managed to jailbreak the iPad after just a day of sales. The crack is a variation on the same "Spirit" jailbreak recently used to de-restrict iPhone 3.1.3 and, like the earlier technique, is believed to use a browser-based exploit as part of a trick to get root access and let unsigned apps run on the tablet. It's not yet evident how easily this could be made into an automated process for regular users.
A jailbreak was virtually expected following the iPad's launch, but the rapid discovery has shown that the iPhone 3.2 firmware used on the device hasn't patched all of the security holes that were present in the 3.1.3 code. Most jailbreaks to date have used vulnerabilities either in Safari or the OS itself to grant unrestricted access. The combination of the risk to users and Apple's own general discouragement of jailbreaking has led to many of these jailbreaks being rendered inert over time with firmware updates.
Source: iPad jailbroken in a single day | MacNN