FUS++ for Mac

From Makaio:

FUS++ is a set of enhancements to Apple's Fast User Switching. Its primary purpose is to replace the bulky, screen-wasting menu item that Apple provides with a more compact one. It can currently be configured to show either a small version of your user picture, your short username, or, like Apple's implementation, the long username.
Other FUS++ features include the ability to run scripts or applications on switching to and from your account. See the website for screenshots and more information.