There's a whole lot more to social networks than connecting with old friends and sharing photos.

The old saying, "it's not what you know, it's who," is really more like, "it's what you know and who knows about it" these days.

LinkedIn is a professional social network that can help leverage your career for business contacts, marketing your personal brand and capturing references. Also, companies where many of us would want to work have profiles and key individuals on the site. You can learn a ton about who you would work with and who you should contact to get an inside edge on a job.

Recruiters and headhunters, who we all know can be annoying to IT workers when the economy is good, are extensively using this social network for finding strong candidates. If you are in the market for a new job, or are in need of something, it's really in your best career interest to be actively participating in LinkedIn.

Take it from prolific blogger, author and managing director of venture capital firm Garage Technology Ventures, Guy Kawasaki. In 2007, he wrote a piece about how to improve the value of LinkedIn that is worth a view. All of the points are still extremely relevant.

Here are the details from his blog:

• Increase your visibility
• Improve your connectability
• Improve your Google PageRank
• Enhance your search engine results
• Perform blind, reverse and company reference checks
• Increase the relevancy of your job search
• Make your interview go smoother
• Gauge the health of a company
• Gauge the health of an industry
• Track startups
• Ask for advice
• Integrate into a new job
• Scope out competition, customers, partners

My take: You have to think like a search engine marketer and optimize your own information. Those who do this well will have many more opportunities than they would otherwise.

You line up a strong accomplishments-centric resume, you ask for and gather positive references and recommendations from peers, managers and direct reports and you document it in your LinkedIn profile--something LinkedIn allows you to do very easily.

Both increasing visibility and connectability are key to ranking well in LinkedIn. The more connections you make, the more visibility you will have. That's important because you want to make it easy for people to find you. As Kawasaki writes: "People with more than 20 connections are 34 times more likely to be approached with a job opportunity than people with less than five."

When you do the math, it's a no-brainer. Take a little time and get your LinkedIn profile humming.