Switching out anything else is easy, but to get a motherboard out you have to:

• Disconnect the power connectors
• Remove all Cards
• Unplug all headers; USB, Firewire, Front Panel
• Storage Devices, Removable Drives
• Sometimes you have to completely remove Hard Disk Drives to get the motherboard out, which means removing the other case side panel
• Unscrew the bloody thing and remove it
• Then unplug the RAM
• Remove the CPU

Then of course you have to do all the above in reverse with a new motherboard. Unplugging cables doesn't take much time, but plugging them back in takes 3 times as long if you want to do a tidy job and avoid constricting airflow.

If the motherboard isn't the problem, you've just waste a lot of time.

Granted, the process is pretty quick for the experienced - all up, you're looking at about 30 minutes work (could take an hour or more for the inexperienced). After doing this 50 plus times however, the novelty wears off.