Over the last year, Facebook has become increasingly dominant in terms of being used as the user identity and login on third-party sites. Last summer, we reported that Facebook had dominated as the third-party login of choice, surpassing sites like Twitter, Google and Yahoo in all realms but one - news. News sites saw users logging in almost twice as often using Twitter.

Now, it looks like another site is gaining ground in another realm. Career-centric social network LinkedIn is growing as the login of choice for business-to-business (B2B) sites, proving once again that users prefer certain identities for certain online activities.

Gigya, a provider of tools for social sharing and third-party logins, took a look at the numbers and found that, since its last round-up of social logins in July 2010, LinkedIn has skyrocketed as the login of choice for B2B sites. According to Rachel Peterson, a spokesperson for the company, LinkedIn has seen increased use as a third-party login ever since it updated its profile API. The site has seen an increase from 3% to 20% in just over six months.

"LinkedIn has a strong case that a single social graph through Facebook is not sufficient," said Peterson. "Professionals want to apply different profile data to business oriented sites and share that content with a different group of people than their FB friends."

So, if you're thinking of taking  your site the way of eHow and forsaking all other logins for the one, true Facebook login, you might want to take a gander at the following graphic and see where your visitors lie. Maybe you should be working on that LinkedIn presence a bit more and Facebook a bit less.