
One of the oldest macs to post so far, I've had to replace my battery 3 times since I bought my Mac, the first two under AppleCare. I upgraded it to 500GB 7200rpm drive and 4GB RAM with Mountain Lion and for 95% of what I do it works like a charm. The other 5% is video related because of lack of hardware video decoding on the 8600GT so HD video sometimes taxes the machine too much.
I do agree with a poster above that Mountain Lion seems to run slower than previous OSs, especially when it comes to hard drive heavy tasks.
ONLY real issue is an LED backlight banding issue that just started, problem posted in another thread on the forum.