Some of you may have heard about George who found his way home 13 years after disappearing when someone traced his microchip. (Everyone who has a dog, cat, rabbit or ferret should have them microchipped even if they are house only pets. I can't tell you how happy we are at the shelter when we have a stray come in who is microchipped. You need to keep the contact information updated, too--many are dead ends.) He wasn't home for long before he was diagnosed with cancer but his last days were with his original family and very happy.

http://www.sciam.com/blog/60-second-science/post.cfm?id=the-cat-that-came-back-after-13-yea-2008-12-12