I am experiencing global system freezes where the spinning rainbow wheel appear and all applications are unresponsive, though the cursor can still be moved around. They are very frequent (every 10 seconds at the worst) and they last between 30 seconds and forever (meaning that I have had to force-shutdown many times). I am running Mac OS X Lion (updated to latest) on a Mid 2009 15" Macbook Pro with 2.53 GHz Intel Core 2 Duo processor and 4 GB RAM (Graphics: NVIDIA GeForce 9400M 256 MB). After some research I formed the hypothesis that it has to do with an incompatibility between Lion OS and the NVidia graphic drivers. I tried to fix it by deleting files containing "windowserver" from ~/Library/Preferences/ByHost and /Library/Preferences/ByHost (as seen in this article), but it helped me only temporarily, and now I am back to the frustrating rainbow wheel. I need help to find out what exactly is causing the problem and how to fix it. Are there any logs that I can consult to discover the source of the problem? Does anyone have suggestions as to how to fix the issue?