Looks like issues described in my previous post (Strange Hard Drive Behaviour On MacBook Pro), regarding plenty of intermittent hangs and beach-balls on a MacBook Pro (MBP) with OX Snow Leopard, can all be blamed on the hard drive. Despite the 'rebirth' I experienced with it, it ultimately just deteriorated again over a relatively short amount of time (about 2 weeks), eventually rendering the MBP once again useless.
I've had a hard drives fail on me before and have known of plenty others, but this is the first one I've come across one that still functions, but has some sort of major handicap. In fact, I still use it externally to successfully backup the MBP, it just takes a lot longer than it should.
So despite symptoms that closely resembled issues described in the threads noted below. My issue was not solved by any amount of software updating or O/S reinstalling.
Random freezing from Snow Leopard - total lock-up for about 30 seconds
INSERT-HANG-DETECTED: System Freezes in Snow Leopard and Leopard