As we have discussed many times before, the reason's to jailbreak your iPad (and more reason's to jailbreak your iPad) need to be weighed before jailbreaking your iPad. As of this writing, there is not an untethered jailbreak available for iOS 4.2.1 on your iPad.
Things that I weigh are the ease or complicatedness of the jailbreak, and the gain of a jailbreak. The Cydia Jailbreak Apps available for the iPad are a major factor to be considered. Here are some of my favorite Cydia Apps on the iPad so far...
It makes opening folders much faster in full screen above the dock and does not have a limit for the number of apps inside each folder. FolderEnhancer is available at $2.49 from the Cydia Store.
This is a nice tweak that allow you to navigate your Springboard pages with a clean overlayed interface. You can set this up for multitouch pinch to display pages and icons. Overboard displays the page thumbnail in three column. But you can also adjust the number of displayed column in the configuration screen. Overboard is available for $1.99 in the Cydia Store.
AirVideoEnabler can push out video from any iOS app (including Safari) to the Apple TV through AirPlay. An iPad with iOS 4.2.1 installed can download AirVideoEnabler from Cydia for free. Check out this video demonstation of it in action
There are definite other great reasons to jailbreak your iPad...what are yours?