Well, have you seen this error message in your console log?
10/3/12 11:52:09.869 AM Safari: CGContextClipToRect: invalid context 0x0
Symptoms can include Safari running slow, showing the spinning beachball of doom for a while, and in some cases Safari just plain crashing…
Well, my investigation points to it being caused by an out of date Safari extension. Open Safari preferences, click on Extensions, and take a look to see what out dated, or unused Extensions you have loaded.
Disable all non-essential extensions, close Safari, and then re-open Safari. See if your Safari experience is any better….
Have any other suggestions? Please feel free to comment below!