They don't teach this in management school, but learning how to build and maintain friendships in the workplace is a skill that can take you a long way in your career.

Just ask the founders of Google and Yahoo! But then again, when friends 'break-up' at work, whether it's a legal partnership, two chefs at a bistro, or heads of a public company such as Disney, it can cause a permanent rift in the relationship. The truth is it's risky to work with friends.

Yet it turns out that working with friends - or befriending co-workers - can enhance your job performance. Nearly two-thirds of employees believe that office productivity improves when co-workers are friendly outside of the office, according to a recent study by Accountemps, a staffing company for financial services professionals.

For many of us, friends are magnets that lure us to a new job and the ties that bind us when we might otherwise break away. Yet balancing the chemistry of friendships on and off the job is often a bit of an ordeal.

"Usually it is friends who take things personally," says Juliana Gidwani, marketing manager at neoIT, a consultancy in San Ramon, Ca. "It's harder for a friend to rationalize business decisions." Gidwani concedes that it's easier to be friendly with co-workers - rather than to become close friends with them.

"It's fun to work with friends, but it's even more fun to start work at a new job and become friends with my co-workers," says John Eckhouse, Editorial Director of Modern Media, a conferencing and branding company in Oakland, Ca. "Good friendships created at work often outlast the job."

In Eckhouse's case, his boss is also a long-time friend and co-worker. "When you disagree on strategy or tactics or who to hire or who to layoff - it can strain the friendship," says Eckhouse. He jokes that it would be tougher if his boss was also his spouse.

Just how easy is it to blow up a friendship at work? I've experienced it before, but then I didn't have the benefit of reading James Mitchell's practical work-friendship rules, which he sets forth in a post called "How to Prevent WWIII While Working With Friends." Do not, advises Mitchell:

• "Drudge up the past. This will get you nowhere.
• Storm out of the room. Leaving the situation won't make it go away.
• Throw your hands up in disgust and say, 'I've had it, I quit!' In most cases, you really don't mean it, so don't say it.
• Think of ways to get even. It may temporarily feel good, but will certainly eat away what friendship existed.
• Apply the war to the friendship. You've heard 'don't bring work home' likewise don't bring work into your friendship."

Do you want to work with your friends or simply make new friends on the job? Despite the possible negative outcomes, if you work with friends, there's usually someone who will join you for lunch.

Rusty Weston, My Global Career • San Francisco, Ca • rusty@myglobalcareer.com • http://www.myglobalcareer.com/