The initial version of ML was terrible on my 2008 MBP but they made performance enhancements and now 10.8.2 works fine. Spending $50 for gb/RAM didn't hurt of course (best investment of my life btw).
You must not have an SSD yet. I highly recommend them.
I'll second that. I put an SSD into a 'poor performing' laptop as a stop gap before buying a new laptop. I still haven't bought that new laptop 2 years later.
I used an SSD to breathe a second life into the late '08 iMac I'm typing this on.
Yeah I was checking them out when I was getting my RAM, I'm just on the fence on how long I want to keep this computer.