Careful calling it an investment though, as it's not one and they aren't allowed to call it that.
GT_Andy - the way it works you pay up to basically become a team member, and your feedback helps create the game (if you are a higher up member you can have more involvement like taking photos, organising deals with licence holders etc). They pay for your services in the form of returns of sale.
In the small print it says you have to help in the creation of the game to see a return, and it has been suggested that someone that paid for a $1000 membership could see less returns that someone with a $100 membership if they didn't get involved in the making of the game.
Edit: Here is an interesting article about how the project got in to slightly hot water for people believing it was an investment:
http://www.eurogamer.net/articles/2013-04-18-driving-ambition-pcars-crowdfunding-and-the-fsa