Is really profitable to advertise in Online social media?

I don't want to be a "party pooper" but, does somebody have real figures that show the profits consequence of advertise, market or whatever term is used for marketing in social networks? Again, I declare myself as an eternal apprentice of this subject, but I think organizations that use social networks as their only way to improve sells aim for failure.

As I commented in Professor Miyazaki's blog, I think e-marketing is one of the mandatory tools organizations must use in order to reach possible customers and let them know the goods they intent to sell, but it's not the only one. Just remember the early 90's when internet bubble started to grow and e-companies began to flourish, based on cheap costs and thin organization structures. The final chapter of this history was the disappearance of these companies because didn't have the structure to back up the sales. Maybe some of you think this has not relation with the subject of this blog, but my point is one organization that wants to sell can't rely just in an internet strategy like social network or even rely just in the internet as the strategy to reach customers; it has to use an integral strategy, because let's face it: customers are more sophisticated now than 20 years ago.

Another point I want to address is the real benefit of social networks as mean to improve sales. I think they can be very helpful in the brand recall, but as I read in Damilola's blog I don't think I'm going to join a group in facebook just to see what Sears has to offers me. If I need a blender, for example, I'll look in the websites of Sears, Wallmart, Kmart and Target (just to mention some of the retailers) to compare brands and prices; and even after that you can be pretty sure I'm going to log into Amazon and e-bay's websites just to get it cheaper. I think social networks are used for social life and unless you are an addict shopper, I really don't think it's going to be very helpful.