Hi John,
I have been a co-owner of a secondhand plane (Gazelle) for a couple of years now, and it has worked fine. We have not yet both wanted to fly somewhere different at the same time! And having all the bills halved is great. We have a joint account where we both place a certain amount per month to cover hangar fees, insurance and 100 hourly. If unexpected bills come up that we cannot cover from the account then we just pay up the extra between us.
I also know of 2 other shared planes at our airfield, both syndicates of 3. So it can certainly work as long as you have the right people, and right circumstances (ie all fly about the same number of hours per year)
Cheers
Neil