I haven't, but they do charge by the hour, so it's in your best interest to have as much information as possible before you ask anything. If it were me, I'd make sure to get the month and year of publication, the copyright owner's name, and any results you can find (like initial registration numbers) from the Catalog of Copyright Entries. Anything you don't give to them, they need to find it to answer the question, basically.
Best of luck!