I have now for 3 months in config 2x2.66, 8coeurs, 4GB of Ram, not more because I installed a Protools HD3. After spending 4 years with ProTools LE and HD1 on pc, I got tired of repeated crashes!
I realize how much I feel confident about leopard, I have not yet found the limit of my system. I do not regret at all windows xp let alone vista.