What information can someone get from the Exif data on a picture?

-I posted a picture of myself on a website, taken with my webcam. People started saying that they were going to get the exif data from my picture and uploaded my picture again saying they found it. What is this? What can they do with that data? Can they find information about me or my computer? Nothing has happened so far, but I don't underestimate these guys. Thanks.