A friend of mine at work is in the Apple Developer Programme, and also has an iPad. At the moment, the iPad is a little behind the rest of the iOS devices, in that it's still running a v3.x.x version of the operating system. Lots of people would argue that that's fine - and my experience so far has been that it's a wonderful device - but anyone with an iPhone with iOS4 on it knows that there are some very useful features which definitely enhance the user experience.
As part of the developer programme, he gets early releases of upcoming iOS versions and he got v4.2 for the iPad and tried it out. It seems apple quality control is not that applicable to their beta releases - his 3G connection was well and truly borked and the mail application crashed a lot.
"Fair enough" thought he "I'll downgrade back to V3"
unfortunately this proved to be a vain hope - it appears he can't get the baseband to downgrade as well, so he's stuck with the dodgy beta or an iPad which won't power up.
So if you're an iPad user and you're on the dev programme - it would appear you need to consider taking the beta release very carefully. Apparently forum postings indicate that the non-3G iPads may have an easier time of it - which might well indicate a problem with the baseband software as, of course, a non-3G equipped iPad probably doesn't have baseband software at all.