there are couple things:

don't know how you are measuring constant 600mhz frequencies. I remember one test case that didn't prove anything. measuring interval 1 second, processor does 600M calculations per second with max rate so what is the frequency 599999999/600000000ths of a second? the measurement of frequency doesn't last many cycles, correct me if I am wrong.

and no one of you probably have know-how about designing circuitry, heat disspatch etc with mobile devices. I am machine engineer and I know enough from thermal dynamics that plastic isn't the best material if you have heat you need to loose... and n900 probably hasn't been designed overclocking in mind: there is no point creating reserves for cooling with mobile devices. it costs, increases device size, ....

and how long have the overclocks been out? If I remember correctly, less than 900.hours since first announced method. So there is no real data about how well n900 lasts when overclocked. and there is no way counterarguing with reports that device runs well overclocked and no failures for now. when you have thousands of hours overclocked, we can get back to it. so it takes atleast a month if someone has used and will use his device 24/7.....

e: and please keep in mind that nokia has to design devices to last 2 years minimum with any usecase (except exceptions mentioned in warranty terms)