Using the new pinch feature of the MacBook Air'/Pro's zooms in and out too way fast - it's so fast it's not controllable. Command +/- or Command 0 is the only way to even try and go back to 100%. Also, when pinching - it does not respect the "Zoom text only" setting - always zooming the whole page.
The multitouch functionality is implemented in Safari, the browser, not WebKit the engine. Safari bugs should be reported at <https://bugreport.apple.com/>. That said, I have no problems with pinch/zoom on my current rev MacbookPro.