Has anyone come across this, and is it a bug? My iMac has 4GB of RAM, and right now I have Safari (3 tabs) and iTunes open (doing nothing but syncing apps to my iPhone). I had 2.99GB of free memory on Activity Monitor, and I went downstairs to prepare dinner and left the Mac running. When I returned some 40 minutes later and checked Activity Monitor again, that 2.99GB of RAM is now showing as Inactive, with 30.8mb of Free Memory available. Nothing else opened, nothing else running. Anyone?