Sometimes, my Premiere Pro in my iMac just hangs; that is, I get the spinning beach ball. This usually happens when I'm playing some clip in my source monitor or moving my current time indicator fast through the clip in my source monitor. When it hangs, I have to right click on my Premiere Pro icon in my iMac dock and Force Quit.
I don't know what the cause is. My first guess is the playback controls in the source monitor, as I said above. At times, I feel like it has something to do with the Auto Save feature where I'm messing around with the source monitor while PPro wants to do an auto save. But I'm not sure.
I have a decent iMac: 2 GHz dual core Intel processor, 2GB RAM.