Next time an app is beachballing, open Activity Monitor, select the app, click the little "i" icon, then click "Analyze process". You'll then get a bunch of st

Next time an app is beachballing, open Activity Monitor, select the app, click the little "i" icon, then click "Analyze process". You'll then get a bunch of stack traces that show you where the process is spending time. To diagnose beachballs, the only interesting thing is the main thread (the first one). Sometimes you can see from the method names where it's hanging.