If you've noticed your time in Windows 7 has been off lately, it's due to the government moving their synchronization server, "time.nist.gov", to a new address. It is recommended you switch to "time.windows.com". Do this by right clicking your time, going to "Adjust Date and Time", and to the tab "Internet Time". Change the settings, and select "time.windows.com" on the drop down menu, or type the address without the quotations into the text entry field.
Edit: In hindsight, I'm sure this effects EVERY computer produced by windows. It is recommended that even if you do not have Windows 7, you still check which server you have your time sync set to.