We do not sell motherboards because TiVo service is tied to the motherboard, so swapping motherboards means your TiVo won't follow it. Typically, it is not a part that is swapped in its entirety for that reason.

Tivo Motherboard Longevity

I don't have any input on the HD version (in fact I am currently having a problem with my unit - but not sure what the cause is yet).

However, the Series 1 units lasted a long time. I still have my S1 and it still works. Even after various disk drive upgrades and replacements (which I did myself). I'd say be prepared to replace the drives frequently over a period of about 7-8 years because the drives are the most likely thing to fail...frequently. BTW, the S1 has lasted about 7-8 years (I can't recall exactly...it's been a LONG time) with drive replacements. Just make sure to take care of the unit properly.

-Donner

Heat is the only real enemy to motherboards (barring a catastrophic power supply failure, very rare).

Anything you can do to make certain the Tivo runs as cool as possible will be a boon to the whole unit, and may even help the hard drive(s) to last longer.