Try it yourself: Leak
So keep restarting your Safari from time to time to reduce memory usage. If you enable the debug menu, you see the memory usage in the "Page Load Test" window at the bottom.
I assume you filed a bug, right?
Of course I did. Filed on 11-01-2003. It was classified as "Performance".
Hmm...maybe I'll file a duplicate just to annoy them :-).
Well, it's still there. I hate the beachball.