What plugins do you have installed? have you got any enhancements installed? what kinds of software do you have installed?
I don't want to go down the entire list. Suffice it to say that I have not installed anything new recently, have not installed some of the other programs mentioned on this and several other threads I've read, experience the problem when nothing else is running except system essentials, and never, ever had an issue before 4.0.3.
One thing I have been able to replicate, however. If I click on an empty side margin on foxnews.com, that locks up the program 100% of the time--spinning beachball forever.
Please, no snarky comments about foxnews.com. It is just one example. I actually had the same thing happen on MacRumors.com as well, when I accidentally clicked on a sidebar before it loaded in completely.
I don't know if that helps. Certainly if there are merely isolated reports of problems, then each one is probably unique. But if many people are having similar issues, it might be a bug on Apple's end.
BTW, that's why the "me, too" threads actually matter. Yes, they suck for diagnostic purposes, but if there is a huge volume of them they can indicate a bigger issue.