In my opinion and experience Facebook ads can work well only if you advertise your fan page. Get people like it (obviously the fan page needs to be interesting

In my opinion and experience Facebook ads can work well only if you advertise your fan page. Get people like it (obviously the fan page needs to be interesting for this), then from time to time post stuff that advertises your startup. It's more work, but you can market to every fan many times instead of hoping she will buy from you or give you her email address from the single visit the ad would bring to your site.