This one is from the “d’oh” category. As recently I’ve moved to Barcelona and since Bucharest and Barcelona are in different time zones, I wanted to set my system’s time an hour back, in order to display the correct time.
I went the easy way: right clicked on the clock in the upper right, selected “Adjust date and time” and made the modifications. After a few minutes the clock was showing Bucharest’s time and my changes were overwritten. I though I must have imagined setting the clock right in the first place – since I “tasted” Moritz thoroughly – and did it again.
I’ve ignored the clock for a while and, later on, when I looked at it, it was displaying Bucharest’s time again 
D’oh! Ubuntu queries it’s time servers from time to time and sets the hour according to the information retrieved from these servers. And since my timezone was still set to Europe/Bucharest, on each update my system was receiving the time for that area. I’ve changed the timezone accordingly and everything started working. Magic!
To change the timezone of on you Ubuntu system go to System > Administration > Time and date. Or, if you’re a console freak, just punch in:
sudo dpkg-reconfigure tzdatain order to set the correct time zone.