what I have noticed is that since installing Leopard back in October, my Macs have had hardware failures. First up was my 12" Powerbook g4 1 GHz where the HD failed two weeks later( S.M.A.R.T didn't pick it up). Around the same time my 20" iMac G5 2 GHz started to randomly shut down. We didn't get it in due to it being once in a while then stopped doing it. But, it has started up again two months ago and has gotten worse this month. I am guessing logic board failure. I am not really blaming Leopard. Just funny my Macs started having problems after installing it.
sorry to hear that though