[ars]

If they got a warrant first I'd be OK with it - as long as they were competent of course and didn't leave the person vulnerable.

It's no different from getting a warrant for a phone tap, or a copy or your US mail.

(Incidentally they don't need a warrant for a copy of the address on the front, called http://en.wikipedia.org/wiki/Mail_cover - so presumably they don't need a warrant to ask your ISP for a list of IP address, but I'd want a court to confirm that first.)