What do Facebook, Foursquare, and Twitter all have in common? American Express (NYSE: AXP) is using each network to broker social transactions, and in the process is proving there are tangible reasons for everyday businesses to get involved in the social sphere.

While each arrangement is different, the essential elements are the same. Link an American Express card to your social network and get access to deals. Here's a closer look at the various options:

Where is LinkedIn (NYSE: LNKD) in all this? Nowhere yet, and I don't expect that to change soon. Retail commerce isn't in LinkedIn's DNA. Nor is social media. Rather, the company is a big data play that's beautifully positioned for how it aggregates and presents career information that wasn't easily accessible before.

American Express goes further by arranging transactions that might not occur otherwise. Everyone wins, giving the soft, murky opportunity of "social media" a hard currency edge. I like the idea enough that I've made an outperform CAPScall on American Express in my Motley Fool CAPS portfolio.

Think I'm wrong? That American Express is the exception and social media is an overhyped, sure-to-disappoint fraud? So be it. Safer choices are out there, including these six stocks that top professional investors are buying now.