Well as I see overclocking your device only avoids waranty if it broke through that. So if your n900 brakes because of the overclocking, waranty of course doesn't count anymore. but if it brakes because of a bad quality, something went wrong with "building" the device, and it has nothing to do with the overclocking, nokia couldn't say anything... I can tune my car with chip to have 500 ps instead of 200 ps. if my radio brakes (bad example) the waranty still is intact, because chipping my car doesn't directly touch the radio. but when my engine brakes because of chipping its my false.
or am i wrong?