My buddy and I did one multi cache, and had some luck with it.
I wont say how many stages it is, since I didn't list in on the cache's page.
It is called the Back and Forth Cache.
http://www.geocaching.com/seek/cache_details.aspx?ID=35751
If I was doing this cache myself, I would wonder if it ever going to end.
I think if I do another multi, it will be no more then four, for a few reasons.
One, the chances of making a mistake grows with each leg.
Two, as a player, I really don't like really long multi.
If you want to know how many legs it is, or any more details of the cache(and aren't planning on doing it) send me an email and I will fill you in