I've been running a game off and on since June or July of 2000. Our group takes breaks for the same reasons as Mr. Yates'. We've probably played around 60 sessions. In game time..... October 1875 to July 1877. I've still got two of the original posse members, a Ranger and a Preacher.
I do want to add, for all that think a long game is a good game, you couldn't be more wrong! A good story means everything and every good story must have a good ending. Just thought I would throw that in, being that we have a GM in our group that thinks if his game lasts longer than everyone elses, it's a better game.