What is MySites ?

A My Site is a Windows SharePoint Services site collection that provides a centralized location for each user to store and share his or her information—such as photos and documents—with other users, set user alerts, and connect with and track other colleagues throughout the organization. My Sites are created when a user clicks on the My Site link on the main page of an SharePoint Server 2007 site.

Users will feel more in control with the new privacy controls introduced in SharePoint Server 2007 My Sites and will be able to more granularly target their personal information. Custom roll-up Web Parts enable users to easily review their sites and documents,and link directly to that content. The ability to easily connect with other colleagues throughout the organization using specialized My Site colleague Web Parts allows knowledge to be more readily exchanged, enabling users to connect to colleagues with similar interests.

Its like companies' internal Facebook network, also MySites are only available to MOSS only