Windows Live Messengers shows up as two separate items in the Windows 7 taskbar. In order to fix this, if it annoys you like it does me, follow the steps below:

1. Open the Start Menu
2. Look for Windows Live Messenger
3. Do not left click, instead Right Click on the icon
4. Select Properties
5. Look for Compatibility Tab
6. There is a drop down list of operating systems you can choose to which the application was compatible (or in the mode you wish it to run)
7. Select either Windows XP SP3 or Vista
8. Click Apply
9. Click OK
10. Restart the application (in this case Microsoft Live Messenger)
11. Should only show one now.

That is it. I can’t explain why this is yet, but at least you can free up some of your taskbar again.