The EFF has put up a page for users to check their IP address or username to see if a subpoena has been issued to gather information on you.

Concerned that information about your file-sharing username may have been subpoenaed by the RIAA? Check here to see if your username or IP address is on one of the subpoenas filed with the D.C. District Court. This information is drawn from the court’s publicly available PACER database and will be updated when that system is updated.

Read More : EFF: RIAA Subpoena Database