It became a habit of mine to always have at least 2 OSes installed on all of my machines - a favorite one (GNU/Linux) and a "expensive-and-buggy" one (Windows 7). It took me a while to notice that the system clock is always wrong in one of the OSes, and when you fix it in one of them, it breaks the other one. It turned out that Windows 7 prefers to use user's local time as system clock, while Linux uses UTC and calculates the offset to the local time. I decided to force Windows 7 to the "the right thing". You need to edit the following registry key value:
...and change its value from "0" to "1". If this registry key value doesn't exist, just create a new one with value type "DWORD" and set it to "1". Now you can reboot and enjoy a synchronized clocks on both OSes.
PS: This information was found on the "Internet", and was copied here solely for my own convenience. I didn't invented this tip, credit should go to others.