Restore your computer to the day you bought it

Unforunately this only works if you do it right after you just bought a computer or after having it restored.  Get that new-out-of-the-box feeling by re-installing Windows using the disc that came with your computer (or do this on a brand new computer).  When you are done, go to Start>Search, type Backup and Restore and set a restore point.  Now you can roll back your computer to a clean setup in the future bypassing the installation process.