There isn't just one social graph, there are many. LinkedIn maintains your professional contacts, while Facebook has friends and family (and yes, often many professional). Twitter has some mix, as well, perhaps with a different filter. Aggregators take these disparate contacts and bring them into one place. A new service uses several APIs to merge them and give tools to better understand and utilize your network of contacts.
Facebook may be this year's most-discussed tech IPO, but last year certainly belonged to LinkedIn. The company, which is turning a modest profit, also has expanded its developer offerings. With that came many more developers to the LinkedIn API, more than doubling the number of registered devs in less than a year. And those apps created on the platform account for billions of API requests each month going to business social network.
Anyone worth their weight in tweets knows the importance of the 'trending topic'. Twitter is an exceptional social tool, not only for witty banter, but for serious business too. Staying on top of trending topics is vital in the attempt to stay current and relevant, and to know what your target audience is talking about. But how relevant are the trending topics determined by Twitter? For the English speaking world; extremely relevant. For the rest of the world; not so much.