Mountain Lion uses like 300mb more on my Macbook Air (probably some of the new stuff running in the background like Notifications) but I don't feel the difference in performance. It's not much slower or heavier than SL during real world usage. It does on the other hand feel better than Lion (I really had regrets when I first switched to Lion, particularly before the bug fixes). But I don't think Lion's problems had anything to do with ram management. Some of the animations just felt particularly sluggish, even if the computer had lots of ram free, and lots of other little things like that.
By not switching to lion and waiting for ML you dodged a bullet.
I had 4gb up until I upgraded to ML. After 2-3 days on ML I noticed my free memory was around 300mb. I upgraded to 16gb for $65(cheap Komputerbay ram from amazon.com). An 8gb upgrade is ~45 for crucial 1.35V ram. I think its worth it.
Cool, thanks for the advice. I didn't even realize upgrading memory was so easy. I have a 2010 unibody, and Apple claims the maximum memory it supports is 8gb. Is that not really "true?"
