This approach seems to have resonated well with users, as the JailbreakMe.com servers have been overloaded with requests recently. The exploit works with all Apple devices running iOS 4 and 4.01, but would not crack the iOS 4.1 beta 2 that is currently in developer's hands – Apple has probably closed the loop on this one already. The hack is free, it's in the clouds, and you are simply encouraged to donate via PayPal.
From what we see on the guy's Twitter page there are still some issues with iPad 3.2.1 constantly rebooting, and with MMS and FaceTime not working properly, which Comex is vouching to address. The solution is totally reversible, too, in case you are worried about voiding warranty.
sources: CNET, Comex