Safari definitely has a memory leak. I frequently defer reading links while surfing via Digg and Slashdot etc, and it’s not unusual for me to have 50 or 60 Web pages on my menu. If I don’t catch up soon enough, the spinning pizza of death takes over and doing anything at all in Safari, even just bringing a different window to the front, begins to take 20, 30, or 60 seconds to complete. At that point it is a race against time to see if I can actually read everything before Safari crashes. (This is on an iBook G4 with 640 MB of physical memory.)
I have submitted error reports to Apple, but nothing seems to get fixed.