I think a hacker would need to be pretty close to you to see your desktop. For example if your wireless connection was not secure and your nabor had sophisticated equipment.
When it comes to internet security, most people are giving their personal information away by not realizing it. Some might throw away a data cd with passwords, or leave emails with passwords in their email box. If you email is cracked your fucked.
Only once I heard of someone chatting and stuff was said, and the next day his family was murdered. It was an Indian family somewhere in New Jersey. Not sure if it was an IP address.
http://en.wikipedia.org/wiki/IP_address