Well, the last time I heard, the new over-the-air firmware upgrade ability that comes with iOS 5 does not work on jail broken devices. You have to connect the jailbroken device to iTunes to actually upgrade the iOS. Someone at the time said it was a "present" from Apple - in that you couldn't "accidentally" update on the iPad itself.
I've not heard anything that says this is not still the same.
So, your only worry is with iTunes. And, as long as you read those little pop-up boxes, you should be okay (Apple will not force you to upgrade - you have to accept the option). Oh, and when you do receive the pop-up from Apple (in iTunes - when the new release is out), there is a box in the pop-up you can check to tell iTunes to NOT ask you to upgrade again. That's what I did so that I don't get pop-ups...
With a little bit of advanced care - and watching out for the new release - you should be okay. Just, keep an eye out for that upgrade so you can head your uncle off at the pass!
Hope that reassures.
Marilyn