I have no plug-ins, nor Saft, nor any Safari hack apps installed.
I do have Flash (as well as Shockwave) installed - using most current Flash version, whatever version that is - but this issue has occurred both before and after my most recent, Flash update.
I also notice, even when a site does not lock-up, that I sometimes get one or several "errors" upon completion of loading.
I ran the Safari 4 beta for quick awhile, and it was less error / crash prone than what I periodically experience now as well as having experienced with the prior Safari version.
So, I feel a bit stumped on what to try next.