Did you hear the one about the lawsuit over Big Copyright wanting personal information from an ISP? No, it’s not RIAA v. Verizon; a woman is suing Comcast because they shared her personal information with the RIAA, and they did so without even waiting for a court order.
In the short term you can prevent this by calling Comcast (1-800-266-2278 or 1-800-Comcast) and asking them to make the information on your account private. I just did it, and like a Slashdot commenter says it was fairly painless (once I got through the phone tree hell).
In the long term, you have to hope the woman wins so that companies aren’t ready to give our information to anyone who asks. Even if that does happen, it’s going to be hard to put the genie back in the bottle. Just look at what’s already out there.