Until now, to add multiple profiles in Google Chrome, you had to use a command-line flag (--user-data-dir="c:\path\to\the\profile") to associate a profile with a folder where the browser will save its state.
In latest, Chrome build, Google added a multiple profile feature that allow user to associate a profile with a specific set of browser windows, rather than with an entire running instance of Chrome. Allowing different windows to run as different Chrome identities means that a user can have different open windows associated with different Google accounts, and correspondingly different sets of preferences, apps, bookmarks, and so on -- all those elements which're bound to a specific user's identity."
Users will be able to associate a profile with a Google account and log in at the browser level.
Google will associate each Chrome window with an identity. "On Windows (and Linux), this's accomplished with a colored and labeled menu-enabled tag at the top of the browser frame, next to window controls. On Mac OS X, window frame is too small to accommodate a tag; instead, we add an item to the menu bar, with a special colored background, in the same way the Windows tab is specially colored."