LinkedIn made big news in the b2b and social media world when it filed for an IPO. The details: for the first nine months of the year the social network doubled net revenue to $161 million. 2010 was also the first time it made a profit.(TechCrunch has a good breakdown of the numbers, including the interesting fact that its expecting revenue growth to drop.)

But what caught my attention was the largest source of LinkedIn’s revenue. Just under $66 million, or 41% of revenue came from hiring sources. Its products from hiring sources increased 178% between 2009 and 2010. Here’s how LinkedIn defines its hiring sources product: “Our hiring solutions are transforming the talent acquisition market by providing unique access not only to active job seekers but also to passive candidates who are not actively looking to change jobs.”

This demonstrates a suspicion I imagine many of us have long shared: LinkedIn is becoming a go-to source for finding jobs. It’s only natural. Social networking makes the job search and hiring process more interactive than the usual job posting sites.

In many ways, LinkedIn is a virtual replicate of the reality people and organizations have long dealt with. Good jobs are usually found through mutual connections. Knowing someone on the inside – or getting in front of them through the brother of your former co-worker – is far preferable method than a blind resume submission. (Case in point: My path to my current job began by reconnecting message on LinkedIn.)

Exciting times are ahead for LinkedIn. I’m looking forward to digging deeper into their SEC filings.