The IP thing is questionable. If someone has a wireless router and they dont password protect it, then someone else can use the signal and the IP addy. There would have to be proof beyond a reasonable doubt. Now remember that cops dont really need a warrant. I dont care what people say, cops do what they want with or without the right.
There has been cases where this faild as a defense riaa/mpaa lawsuits the judge had tossed this defense of an unsecured wireless saying it was the defendants responsibility to secure their network and are there for responsible for anything done from it.