With the iPad 3G in the wild, the long awaited iPad jailbreak has been released. Spirit is a "userland" jailbreak, meaning it exploits a security hole that affects all devices, not just jailbroken ones. This means Apple is likely to release firmware that patches the exploit very shortly - read on for why this is important.
Last year, Apple started "signing" firmware updates, and will only sign the latest firmware - which means they can prevent you from rolling back to older, jailbreakable versions of the firmware. There are ways around this, but they require something called an SHSH blob, essentially your device's unique identifier.
Once you've done this, you'll be able to roll back to OS 3.2 at any time. So, if you're brave, head over to spiritjb.com to start jailbreaking.