Mountain Lion is a memory PIG! Period! I have a MacBook mid-2009 unit with Mountain Lion installed. Under moderate use it does OK, but if I start bringing up more memory intensive applications like Safari, iPhoto, etc, simultaneously, Activity Monitor indicates I'm basically running out of memory (Page outs increase radically). The unit only has 2GB on it (only...really ONLY 2GB?? That's a lot of memory). In any case, I think the solution is clear: MORE MEMORY. I found it interesting that MacTracker indicates that this unit can handle 6GB of memory, but there's no such thing as a 3GB memory stick to the best of my knowledge, which leads me to believe they're talking about installing a 4GB module in one memory slot, and a 2GB module in the other. I really don't think I necessarily need 4GB of memory, and would like to try out a 1GB and a 2GB combo, yielding obviously 3GB of memory. A lot of documentation states that the memory modules sizes need to be matched (in other words, you should use only 2 identical memory modules, like 2 2GB modules) I really don't like wasting money on what isn't needed. I'm not the type of person that leaves a billion applications running at the same time even when they're not in use. If I'm done using an application, I shut it down completely. My question is simple: If I go out and buy a single SODIMM module of 2GB and use it to replace one of the 1GB SODIMM's in my system, will this REALLY create any problems? Thanks!