I know of several people out there that have multiple profiles for the same web site. For example, if Tom wanted to be able to have two different e-mail accounts at Gmail instead of one. Before you would have to use multiple browsers or do the logout and login dance to check them both. CookiePie looks to allow you to manage multiple cookies in one browser window.
The CookiePie extension enables you to maintain different cookies storage in different tabs and windows. To give you a better idea of what that would look like in action the creators of the extension have put together a video of CookiePie in action.
All in all, I would say this extension looks very promising for those who need to do multiple logins to the same service with little to no problems at all. If you are interested, I would encourage you all to check out the official site for the extension so you can learn more about what CoookiePie could do for you.