It doesn't seem like subresource loading is getting throttled, so if a script changes the 'src' attribute on an image repeatedly, it chews through memory and eventually crashes.
Test case will follow.
Created attachment 26780 [details]
Causes unbounded memory growth
This test burns through memory (then crashes) in safari.
In IE7 and FF3, the memory consumption levels off.
This is also the cause of a significant Chromium memory leak and crash: http://code.google.com/p/chromium/issues/detail?id=36142
See also https://bugs.webkit.org/show_bug.cgi?id=31253