Before entering into a partnership, keep in mind that it is often easier to sell an entire aircraft than a fraction thereof; especially if the aircraft is 'exotic' (cf. 18greens' Hunter comment), or based in a location somewhat distant from large population centres. I have seen other agreements with clauses like the one summarized by bookworm, and I think they are fair and equitable to all parties.
In an aircraft share be prepared to lose everything you put in. Anything you get back at the end is a bonus. These are not sound investments like bricks and mortar. They should retain their value but don't be surprised if they don't.
The above may sound awfully harsh, but really it's good advice. That said, although you should psychologically prepare for the worst, many syndicates operate without problems, particularly in cases where the aircraft concerned is relatively simple and inexpensive to insure and maintain. In my experience, problems are more likely to arise where the aircraft is susceptible to hefty maintenance costs, or where one can anticipate disagreements about how much upgrading is warranted (avionics, GSP, interior, props, exterior paint, etc.).
P.S. If you have experienced multiple redundancies in your industry, personally I wouldn't even consider entering into an aircraft partnership unless and until I had first built up - in addition to the capital cost of the partnership share - a sufficient liquid cash reserve to cover at least six months' living expenses, including monthly partnership fees.