Social Network Sites (SNS) as a part of Web 2.0 gain increasing importance in social life. There are different types of SNS being more or less adapted to the requirements of professionals. For a selection of six SNS features and services were regarded in respect to the applicability in the professional life, using medical physicists as an example. Services as groups, calendar, literature services, and career functions prove to be of particular convenience. As all Web 2.0 services SNS depend on the contributions and operations of their users.