The glory of friendship is not the outstretched hand, Nor the kindly smile nor the joy of companionship; it is the spiritual inspiration that comes to one when they discover that someone else believes in them and is willing to trust them.
I think it all depends on your target market, the product/ service you offer and how you go about your advertising. I have heard that facebook advertising provides very low conversion rates.
A lot of companies have tried Facebook ads and found the rates high and conversions low. Facebook needs to completely up their game if they intend to compete with the likes of Google or Microsoft for share of advertising spends.
My opinion is before doing marketing through a social network you will have to get familiar with the features in that social site. Then you will find many ways to promote your business through that site.