Greenpois0n has been released that jailbrakes all ios 4.2.1 devices.
However I tried over 20 time to jailbreak an iPad on a new i5 Macbook Pro with it failing everytime. Tried on my 8 Core Mac Pro and it worked first time. Seams like a USB problem as there both running 10.6.6 in 64 bit mode
Here is the new version that supports the Verizon iPhone
Here is another new version that supports the Apple TV 2
Another Version now fixes iBooks and Apple TV 2 Wireless Problems
PwnageTool 4.2 for iOS 4.2.1 has just been released. Fixes iBooks problem