I don't know if any one noticed this but the leak is actually related to pinch to zoom. I can easily replicate the problem. Just launch Safari and load a page. things that are graphic and flash heavy eat up more memory. Now open up Activity monitor and watch the memory usage.
Pinch to zoom into the Page (being sure to let go) and pinch to zoom out (and let go again.) I found Each zoom eat about 10 MB. May not seem like a lot but those that use this feature often will soon find themselves without memory.
A few things that might play a factor
1) Available memory
2) Page content
3) Screen resolution (I run 2048x1152)
Obviously this is pretty specific to people on MacBooks or who use the Magic Trackpad. this would be why not everyone sees the problem or why it only happens on certain systems.
I tried reporting this to apple but they just kicked it right back to me.