Mission Control was touted by Apple prior to Lion's release as a feature that would increase OS X user productivity by providing quick access to various windows and apps. Instead, many users have found the feature lacking, specifically lacking the ability to rearrange desktop spaces and full-screen apps in their order of preference.
With last week's release of the second maintenance release of OS X Lion, OS X 10.7.2 brings with it the ability to rearrange desktop spaces and full-screen apps by simply dragging and dropping them.
Rearranging items is easy, but if you are accustomed to the feature not being present, and you didn't read the full release notes of the 10.7.2 update, it's something you might not discover on your own.
Launch Mission Control either through gestures or the Mission Control icon. Decide what order you would like your desktop spaces and full-screen apps in. For demonstration purposes, we are going to move iCal to the last position. To do so we click and drag the iCal thumbnail to the right, toward the end of the row.
While you are dragging the thumbnail across your screen, it will take on a transparent look. As you move past a space or app, it will shift automatically.
When the space or app is in the position you are happy with, drop it in place.
If you had previously set Mission Control to rearrange items in order of last used, you will need to turn it off if you want the order you placed spaces and apps in to take remain in place. You can do so by visiting System Preferences > Mission Control.