This is an infrequent issue I've had, but it has happened more than once in the last few weeks that I've been using CS6 on a regular basis:
On occasion, my spacebar will just stop working in Illustrator CS6, so I can't use the hand tool or zoom or… you know, type, basically making Illustrator unuseable. Now, I'm PRETTY sure it has nothing to do with my actual keyboard, because the spacebar will continue to work just fine in every other application even after it does this.
The only fix is restarting the computer. Just restarting the application doesn't do it. Deleting the preferences file and restarting doesn't fix it. It's really perplexing.
Now, I'm NOT certain about this, but I think it might occur after waking from sleep (but not immediately, so perhaps it's unrelated). If/when it happens next, I will attempt to see if I can reproduce the issue, but so far I have no idea why it happens; it just seems random.
I'm using a late 2008 MacBook Pro with 8GB of RAM, running Mac OSX 10.7.4 and Illustrator CS6 (16.0.0, in case people see this after an update has been released).