At some point, Google added an option that allowed you to open a new window and use a separate profile, but it was quickly removed. According to a design document from Chromium's site, this feature be available again.
"The multiple profiles feature will allow the 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 are 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. This is a great feature for Chrome OS, but it will also work in Google Chrome.
Google will associate each Chrome window with an identity. "On Windows (and Linux), this is accomplished with a colored and labeled menu-enabled tag at the top of the browser frame, next to the window controls. On Mac OS X, the 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."
{ spotted by François and David.}