The best thing to do - if your iPad is jailbroken at the time you want to do the update - is to put the iPad into DFU mode (sticky here: http://www.ipadforums.net/ipad-hacking/27489-dfu-mode-dummies.html) and then do the shift/restore thing. Just make sure you've got the iOS 5 IPSW file downloaded so you'll have it handy to point iTunes toward it.
May make life a bit easier...
Marilyn
May make life a bit easier...
Marilyn