BTW....in case anyone is now wondering:
5) Patent expired. After the patent expires, the patent owner has no further rights, although infringement suits can still be brought for any infringement that occurred during the patent's in-force period as long as the suit is filed within the time required by law. An expired patent remains a valid "prior-art reference" forever.
http://www.inc.com/articles/2000/03/18174.html
GLTAL