There's a long article in the Times today that talks about this type of service.
http://www.nytimes.com/2008/05/18/realestate/18cov.html(excerpt)
Electronic communication in residential buildings has gotten a lift in the New York region in recent years with so many new condominiums hardwired for the Internet.
But the means to connect residents in buildings of any age can be as simple as creating a Google or Yahoo group, building a group on social networking sites like MeetUp or Facebook, or joining a site like LifeAt.com, which allows members to post profiles and pictures. Another Web site, MeetTheNeighbors.org, is free to join and largely functions as a message board for people who live in the same building or the same neighborhood.
The buildingwide systems have allowed residents to get to know one another, to communicate with building management, to request and track repairs that must be made and to settle disputes.
LifeAt is used in 149 buildings in Manhattan, according to the company. Buildings pay a one-time fee of $6,000 for access to the site. Residents can post personal profiles and classified ads that can be seen by others in the same building, as well as rate local businesses and receive coupons from national retailers like Kohl’s and Sears. The building’s staff members can also contact residents through LifeAt.
In January, Ryan James, 29, moved into Eleven80 — a 317-unit luxury rental at 1180 Raymond Boulevard in Newark that opened in August 2006 — and signed up for LifeAt.
“I was surprised with the level of participation,†said Mr. James, who is vice president for financial services at Unity Financial, on Wall Street. “It goes to show that people are willing to extend, if not friendship, some level of acquaintance and familiarity. In all the buildings I lived in, particularly in New York City, people kept to themselves.â€
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Click link above for entire article.