I have an MBP 8.1, early 2011, 13 inch, Mountain Lion. Whenever I leave it on for more than a couple hours, I get serious execution lag on every command. For example:
I click something (a link, button, command, even a tab in the browser) and the rainbow wheel of death shows up. After a couple seconds, my command gets executed. I click on another app, and the app does the same before warming up for use - rainbow wheel of death, couple seconds of stall, revival, work. Text edit and preview are sickeningly slow in opening the very smallest documents, so I've had to stop using them completely - the forced version control of 10.8. is not helping in the least. Whenever I do anything I get this rainbow wheel of death lag prior to execution, and what's interesting is the fact that
a) The CPU usage NEVER spikes above 10% (I have it on scree at all times)
b) I actually have free RAM while doing this
I can find no processes hogging up the machine, and there are no fatal errors in the console showing up.
I use it for web development, so I have the following apps open at all times: a Java (I know, death to any machine) IDE running (PhpStorm), Chrome, Sparrow for mail, Twitter client and TotalTerminal.
That's all the apps I'm running. Any ideas?
I'm willing to try anything except sending it to an Apple store for diagnostics and service.
Edit: Additional info: This is a mint condition MBP, formatted a mere three months ago to Lion and upgraded to Mountain Lion some weeks ago. It has 4GB of RAM.
Final edit: I have installed Ubuntu alongside OSX, on the same hard drive. I have also installed all the apps I use on OSX. Ubuntu FLIES, the difference is enormous. Not a single lag, in clicking, rendering, indexing, nothing. Conclusion: OSX just sucks.