I think c3d is right in that Lion and Mountain Lion are slower than Snow Leopard if you don't have an SSD. It seems to me that recently Apple have been designing OSX with SSD-equipped computers as the target. They assume that you will have fast read times, and use algorithms to optimise that. For example, they 'deactivate' applications that aren't being used, because they know they can restart them from SSD very quickly, which in turn frees up physical RAM, which speeds the computer up elsewhere. The problem is that if you don't have an SSD, this decision is catastrophic for performance. As always, Apple are skating to where the puck is going to be, not where it is...