It can make your system un-upgradeable without (apparently) any means of undoing it other than a complete reflash (which is ironic, as this upgrade was supposed to make reflashing redundant). There is no warning other than that your tablet doesn't reboot at the end of the "upgrade" and it's impossible to say what will trigger this bug. Of course, because this doesn't happen to the majority of users, it's officially not a bug and you're supposed to remain very schtumm about it. Well, that's at least what I got from a Nokia dude's post... So, the question is: Do you like playing Russian roulette?