"In other words, it is a violation of 35 U.S.C. § 292 to intentionally mark an item in commerce with a patent number that has expired or that does not protect the item. ... In Forest Group, Inc. v. Bon Tool Co., the Federal Circuit ruled that the $500 maximum penalty attaches to each individual article that is falsely marked..."
—FDA Law Blog, 3/7/10
Yikes. I don't have any special insight or expertise in this situation, but this struck me as a pretty important link to pass along. If you mark a device "patent pending" it appears to be pretty important that you actually file a patent application. The days of using the term as an empty threat may be ending.