We started with one simple model under the assumption there's a "best" model. Now we're discovering there's more than one "ideal" model - different models work better on different sites (although some things work well consistently, and some things consistently don't). For example, on some sites providing an incentive for the referrer increases conversion (not surprising).. but on other sites, it hurts conversion - the social value of altruistically sharing a good deal outweighs to social cost of sharing something to your own benefit.

Now our product vision is to offer a small variety of simple models proven to work well, to get people started. But we also let hackers tweak stuff so it can work more seamlessly with their products.

Allan