Answers:
Very little, in actuality.
Your ISP issues your IP Address. And most general public enjoy a dynamic IP address that your ISP change every 24 hours or so. Pretty useless to anyone.
In the USA, the individual method to take an ISP to release personal information ( autograph, cellular phone, address etc.) roughly a selective IP address is near a Court Order.
And Court Orders are usually single given out surrounded by the grip of serious criminal commotion.
I wouldn't hold my breath.
I'm not sure you can hack into someones PC w/ purely within IP address but if some one get yours consequently can find out be your Pc is hooked up(i.e. your home address and/or department.) I'm not what else they can do or even how to bring ahold of you personal IP address. But they look something similar to this 123.4567.898.76. (not sure how long)