Have you raised money from your friends for your startup? 
RobGR: You will have to research the law yourself, but there is a limit to how many people can invest in a business before you cross a line into "selling securities" and have to formally be a real corporation with stock.  Not that you can't do it, you just want to be aware of this and do it correctly.  I think the Nolo books on incorporation should have the information.