How to fix OS X Lion being unresponsive?

Solution 1:

This kind of thing is a RAM problem 9 times out of 10. Your RAM is constantly being paged in and out to your (relatively slow) hard drive, causing you to wait. THe best solution is to upgrade your RAM or if it's already maxed, consider getting an SSD.

Solution 2:

I have a 2.16 GHz Core 2 Duo iMac that recently had this problem (I suspect it was caused by too many windows open under Safari) and I had searched on this site for a possible fix. Nothing I tried worked, so I unplugged the iMac and planned on taking it in for a repair. I got to thinking about the possibility that the mac's internal battery may be preserving the condition, preventing me from recovering from the freeze. After having the Mac off the mains for 24 hours, I re-plugged it and fired it up and the freeze was gone. I don't know if this was just dumb luck, but I don't have the freeze anymore.