I think the big kicker is whether or not the owners are always riding on their own plane or not - the actual airplane they own a piece of. With many large fractional set ups, an owner may own a piece of "a" Citation (example, N123AB) - but may never ride on THAT particular Citation (N123AB), just an identical one that the fractional company operates - they operate a bunch of them and you just get which ever one is closest/convienent. This set-up pushes the whole operation firmly under 91k (fractional).
I know of a bunch of multiple-owner airplanes (2, 3, or 4 owners) in which a single crew flies the airplane for all of the owners - operated under 91 - but the owners in this case are always riding on their own airplane. Don't know of any planes with 30 different owners, though.
Boiler brings up a good point about making sure the tax-man is happy with the arrangement.
Last edited by Likeabat; 08-14-2010 at 07:40 PM.