I have been building computers for myself, friends and relations for about 8 years and have never trashed a motherboard, even when I have had to flash a BIOS.
But there is a first time for everything.
My test machine is in a Silverstone case and it is a really quiet computer, so when i upgraded my main computer I used the 7600GT card to upgrade my test computer.
As the Silverstone case is a very tight fit, I did not notice that the lugs of the Zalman fan I had fitted caught on the heatsink cooling the chipset and lifted it of.
The machine ran for 3 months like that then died.
Still it has given me a valid excuse to upgrade it now.
If anyone is using a Gigabyte 939 motherboard with the chipset heatsink next to the PCi-E slot, do not modify the fan on the graphics card.