I noticed that if I use OSX for a while, I get really low on memory and things start to get slow. I have been suspecting that something was not quite right, because in Activity Monitor I would look at the memory usage and it didn't seem like I was using that much memory.
I added up all the memory from all processes shown in Activity Monitor. It adds up to only 1769.2 MB, even though I'm supposed to have 4GB memory. I only have 100MB of memory free. Why is that? It's showing 625MB as wired, 1.63GB as active, and 1.65 GB as inactive. It says that 3.90 GB are being used.