Everytime somebody makes these posts I groan. :frown:
If you live in Alaska and it's cold inside then your system will run cooler than say living in warmer Florida.
I live in HK and my "measured" CPU temp varies by as much as 10 degrees thru the year.
The thermistors are also not very accurate, the only way to have an idea if you system is too hot is to run at standard speeds and then record the temps - try this at various times of the year/temps or whether or not you have the heating turned up or the aircon on full blast - these situations will make a huge difference.
Then try running the same situations with your CPU overclocked to see what the difference in temp is.
It is a good idea to know you are running within "spec" of the CPU operating temp - but don't always think you need to achieve the readings some of these guys are getting.
The Duron can run at temps of upto 90C, 50+ is quite normal here in Hong Kong with my friends systems.
Even assuming your system and your friends system are running at the same ambient temperature and he is running at 20C less, all that "might" mean is his thermistor is not in full contact with the CPU or that his is less accurate than yours. Of course maybe your cooling/airflow is not so good?
It could also be that your thermistor is reading too high 
 
There was a lot of chat about this subject back in the C300A @ 450Mhz time.
I ran my overclocked CPU at 300Mhz then 450Mhz - the temperature difference was 1C for any given time of the year - not much to worry about if you ask me. 
Also the best way to decrease temperature that I found was to install and extra exhaust fan at the top rear side of the case. That way you are increasing the flow of hopefully "cooler" air thru the system.
One of my friends decreased his measured CPU temp (Duron 700) by 10C by buying a new case! Must have been an airflow problem presumably?