Windows 7 automatically pins Windows Messenger (Microsoft's Instant Messaging service) to your taskbar. It takes up system resources, runs on startup and uses system memory. Plus, there are better IM clients out there (Digsby, ICQ, etc.).
It can be a hard program to hunt down and uninstall. Here's how to get rid of Messenger in Windows 7.
Go to the Control Panel. Select Uninstall a program.
Scroll down the list of applications. Select Windows Live Essentials.
Chose Uninstall (don't worry, this won't uninstall all of your Windows Live components, just the ones you choose).
Check the Messenger checkbox and click Continue.
That's it!