Your PC might be a shared one and used by multiple people and in such cases whenever you need to switch user, it is quite a difficult process as you need to open start menu and then select the switch user option and then wait for the PC to actually switch. Fast User Switch is a freeware and portable tool for Windows which allows you to switch user just with a click and the process is really fast and you do not have to open the start menu for switching user.
The app is an exe file and when you execute the file, it fires the switch user command in Windows. The advantage of using the tool along with Windows 7 is that you can actually pin the app to the Windows 7 taskbar and hence you can simply click on the button and switch the user.
Although the app works perfectly with Windows 7, you can also use it on XP and Vista and add it as a quick launch item in the taskbar.