The online social utility phenomenon has enticed more than 550,000 people, about 10 per cent of the Greater Toronto Area population, to join the network, making it the largest of any city in the world.

Facebook originated at Harvard, and is the sixth-most trafficked site in the U.S., but Toronto's network now has more members than Chicago's and New York's combined.

"There are a lot of colleges and universities in this town and as we know Facebook was a site that has its origins in that community," said Rick Tremblay, with Youthography, an advertising company that targets youths.

Students also join their school networks. More than 100,000 people are connected to Facebook through the three universities in Toronto alone.

Some sign up for their school but not their region, so the number of Torontonians on Facebook may actually be higher.

"I think the sheer student base has contributed to Facebook's overall popularity," Tremblay explained.

In just three years, Facebook has gone from a student-oriented site to a must-join for those who want to stay in the virtual loop.

Now school kids, young professionals and socialites alike us it for business-and pleasure. It's joined the ranks of RIM's BlackBerry, or 'CrackBerry'-It's been dubbed 'Crackbook'

The Ontario government, concerned that its employees were spending too much time on the site, banned it from its office computers last week. Thousands of civil servants came to work only to find that Facebook had been blocked like porn.

Toronto officials followed suit, announcing Wednesday that the city's 23,000 employees, with the exception of councillors, won't be able to Facebook while they're on the clock.

The union representing provincial managers, AMAPCEO, protested the ban.

Union president Gary Gannage said Tuesday that the majority of government employees are "trustworthy, hardworking individuals."

But Premier Dalton McGuinty backed the decision. He said he doesn't see how Facebook adds value to a workplace environment.