What would you do?
Well I can say I would have a lot of fun haunting people, possessing them or just scaring the crap out of them.
I would of course spy on people, because it would be funny to spy on the government for once, not to mention all the secrets I could learn....
I also would explore space, as I imagine a ghost could travel pretty fast, and that would almost never get old as there are so many amazing things to see out there.
Keep in mind this is all hypothetical, even if you don't believe in ghosts (I actually don't myself), you can still participate in this thread.