As far as I'm concerned, the commercial real estate market just got it's first social network.

MyDealBook was released three weeks ago in the US. One of the founders is Ryan Slack, former CEO of PropertyShark (an information service for the commercial market), and the service also hits the ground running with adding the existing 300 000 PropertyShark users automatically to the network.
The idea for the service is (according to an Inman interview) a spin of from the user needs at PropertyShark;
"As CEO of PropertyShark, I found that our users were demanding that we let them meet other users: They demanded the ability to advertise on the site and they demanded more networking functions. MyDealBook addresses these needs",
MyDealBook is described by this Reuters article as:
"MyDealBook.com combines the best social networking techniques with powerful tools specific to the needs of real estate professionals. Its features are designed to help users expand professional networks, find new business and manage projects. Features include user profiles, messaging, networking and marketplace listings, as well as:
Deals -- features a unique deal management system that allows users to post their professional activities to gain credibility, promotion for their projects, seek funding, market properties and share files
Mini-feed -- provides users insight into the projects and deal flow within their network
Events -- lists opportunities for real estate professionals to connect in person, including networking mixers, speed networking, conferences, training, site visits, fund raisers, sporting events, and more
Groups -- enables users to join or form their own groups for specific purposes, such as organizing events, sharing deal information, collaborating, forming company teams, office networks and investment clubs
Natural groups -- automatically groups users by company, profession, location, educational institution, professional association, state licensing and professional designation, to allow easy search and identification of
potential clients, business partners, or service providers
Services -- provides powerful tools to search and match users with complementary business partners
Jobs -- provides its users with opportunities to find or advertise job openings specific to the real estate industry.
A niche not covered by Costar?
In this article in New York The Sun an associate director at the commercial real estate firm Newmark Knight Frank said the site could fill a niche not covered by services such as CoStar, the subscription-based Web site commonly used by office leasing brokers that offers only limited information about other industry professionals.
Find out more
About MyDealBook here;
GeekEstateBlog - an interview back in September
4realz - have both a pod interview and a post about it
Inman coverage is found here and here