I've been in a group of four with a C120 for 7 or 8 years now, the other members have come and gone over that time; I'd say it's a great way to go if you keep a sesible head on. We paid £17K for the aeroplane and currently charge £35 pm and £25 per hour wet. Lots of fun and very cheap flying.
Make sure you know who you are geting involved with, keep the number of shares low (both to improve availability but, more important to reduce the risk of people you don't know very well doing things which will cost you lots!) and be prepared to do your shere of the comunal work (I do the accounts and am the group FI, another guy does the engineering etc etc). I'd recommend a simple aeroplane too as this reduces the risk of expensive mistakes.
Happy landings
3 Point