When the folks at travel company Sabre Holdings saw how people were using their new Bambora travel advisor, it got them to thinking.

Bambora is a simple social network for travelers, one of many products Sabre Holdings has developed for the travel industry. It uses a basic question-and-answer interface, so travelers can submit questions like “What’s a good hotel on Mykonos?” to the community of members for answers. Answers are captured to a searchable database for posterity.

Sabre built Bambora to be a public-facing product, but managers immediately saw its utility within the company. As Sabre has evolved and diversified over the last few years, its employee base has become fragmented across the world. This has challenged Sabre to manage projects and sustain teamwork among its 9,000 employees. It had become difficult even to keep track of which skills existed within the far-flung organization.

From Bambora, SabreTown was born. The internal social network is now widely used by Sabre Holdings employees to find expertise that would otherwise have been buried within the organization. Questions entered into SabreTown are processed by a relevance engine and built into employees’ personal profiles. Sabre is effectively creating a massive knowledge base that employees willingly populate with their own information.

“This is an online hallway,” says Al Comeaux, senior vice president of corporate communications at the travel firm. “It’s an opportunity to build a culture.”

It’s also a chance to capture and preserve corporate knowledge. That’s becoming an increasingly pressing concern in U.S. companies. The ratio of U.S. citizens under the age of 65 to those over 65 is expected to decline from more than 7:1 today to about 4:1 by 2030. Businesses are scrambling to preserve expertise that can be passed along to the next generation of employees. (See How to Build Your Own Wikipedia and Three Things the CIA Learned About Implementing an Enterprise Wiki.)

That has IT and human resource managers looking to the Internet for solutions. And like so many recent Internet trends, the phenomenon called Web 2.0 or social media is finding acceptance in consumer markets first before working its way inside the corporate firewall.

Nearly everyone is familiar with the stunning success of social networks like Facebook and LinkedIn, which together count nearly 100 million members. Now big businesses are adapting public services to their own needs. Forrester Research estimates that the market for internal social media applications will reach $4.6 billion by 2013.