Ask a room full of college students and a room full of business professionals “Who belongs to LinkedIn?” and the results will be almost a mirror opposite of each other. Facebook is the social network for after-hours fun. In contrast, LinkedIn is for business professionals. It’s a buttoned-down, no-nonsense business destination with a two-color, text-heavy design that almost screams “Boring!”

LinkedIn is anything but boring, however. Its value as a way to establish and further business relationships is unparalleled, thanks to the unique services it offers. If you signed up long ago and forgot about it, I recommend you take another look.

Like any social network, LinkedIn has personal profiles, groups, and the concept of “friends,” which it calls “connections.” Its most distinctive feature is based on these connections: a six-degrees-of-separation structure that enables members to connect to people they don’t necessarily know through intermediaries within their trusted circle. It’s the online equivalent of arranging an introduction.

Personally, I don’t find this feature all that useful, but connections are the core of other LinkedIn features that I do like.

One is Answers, a section where members can post their questions about nearly anything to a select group of connections or to the entire membership. Answers is a great way to get questions resolved quickly, but it’s also a means to expose your skills. Believe it or not, some people answer more than 200 questions a week on LinkedIn. One reason for their generosity: the site enables members to rate the quality of responses and showcases the most prolific contributors in a Hall of Fame section (the all-time leader has answered an incredible 14,000 questions).

Company Research

LinkedIn is also unparalleled in its database of company information, but it takes a bottoms-up approach, focusing not on corporate leadership but rather on individual employees. If you need to find a specific person within a company or just check out a potential partner or employer, you can go in through the back door by consulting current employees. LinkedIn will tell you if you have a direct or second-degree connection to the people you seek.

Job listings go beyond the standard titles and description to provide contact information for people within the companies that advertise opportunities. If a job interests you, you can click through to find out who you know at the company and then contact that person for insight or a referral.

LinkedIn also excels at search engine performance. Its public profiles do so well on Google that they frequently outrank personal websites in search results. I don’t know the secret, but I suspect that the site’s system of internal links is partially responsible. This alone is enough reason to set up your personal profile.

Given all this career-boosting utility, it’s not surprising that traffic to LinkedIn reportedly doubled in the weeks following the stock market meltdown. Members can brush up their personal profiles by swapping recommendations with others, updating their qualifications and showcasing their expertise through integrated applications. Unlike Facebook, LinkedIn keeps a tight rein on the applications it chooses to support, limiting the current selection to just 10 business-focused services.

While LinkedIn doesn’t have nearly the membership numbers of Facebook, its business focus is an advantage. The CEO was recently quoted saying that the demographics of LinkedIn members are better than those of Wall Street Journal subscribers. In troubled times, that’s a very good place to be.