KANSAS CITY, Mo. — Minutes after attending a seminar titled “Use Social Networking to Your Professional Advantage,” I opened my e-mail and found two new invitations to join LinkedIn.com networks.

One request came from a person I’d had professional contact with previously. I clicked “accept” and quickly went on to other things. I didn’t recognize the other name, so I closed the e-mail without response. And, thanks to Ellen Levy, I didn’t feel bad about the tacit rejection.

Levy, vice president of corporate development and strategy at LinkedIn.com, had just presented an overview of Internet social networking sites to several hundred people at the Central Exchange’s annual Women’s Lyceum, an educational and networking event.

Understanding that attendees came to the conference from many different backgrounds and levels of Web familiarity, Levy prefaced her user advice with a primer.

First, she explained, there was Web 1.0 — the mostly one-directional flow of information over the Internet. Think of Web pages.

We’re now in the age of Web 2.0 — an era of two-way communication that in the last three years has spawned a host of interactive social networking sites.

A show of hands indicated about half the people in the room used LinkedIn, a professional networking Web site.

Even if you’ve never been on a social networking site, you understand the concept: It’s a cyberspace handshake. It facilitates connections. It does what Rotary meetings, telephone calls, cocktail parties and e-mail have done for years.

Let’s say Joe wants a job at Hallmark Cards. Joe doesn’t know anybody in the human-resources department or in the target department where he wants to work. But Joe is good friends with Sally, who has a Hallmark Gold Crown store. Sally knows many people in Hallmark’s retail division. One of them, Bill, is the main liaison with Joan in the human-resources department. And Joan knows that Fred is exactly the right person for Joe to meet. Fred, meet Joe. Joe, here’s Fred.

I made up that scenario, but that’s the six-degrees-of-separation concept.

A professional networking site might help make the who-knows-whom connections that have always been an essential ingredient in job hunting, business development and sales prospecting.

(A user also can get a wealth of professional responses quickly when posting a question on the appropriate area of the site.)

A LinkedIn connection may not make sense if you accept an invitation to join one’s professional network if you don’t know the person or don’t have ties to one’s business skills or services.

“It should be a tool to leverage relationships you already have,” Levy emphasized.

A professional networking site can be a good way to put your business profile — basically your resume and the services you can offer — online, where they can be seen by millions of others.

But, as much as Levy championed the professional development possibilities of Web 2.0, she reminded attendees something that most knew well:

“Time is a scarce resource.” Use networking sites judiciously.

And, most of all, she said, don’t get sucked into making a contest out of how many “connections” you can list. It’s not a matter of quantity; it’s the quality of relationships that count.

Diane Stafford is the workplace and careers columnist at The Kansas City Star. Her blog, workspacekc.typepad.com, can be reached at stafford@kcstar.com.