Co-founding
ninjaa: As someone who has been screwed before: 
Make a buyout date and clause. Value the IP based on time, calculate your share and set an end date on your agreementpast which you can demand cash from him for your stake. This way he may have final say on all issues, but if you disagree with the general direction after a couple months you can deal him a punishment by demanding a cash out. It is vital to set said date and amount in writing at the outset.