Earlier quoted context omitted.
It's a smooth effect, but it's so much nicer when scrolling scrolls instead of zooming. On this one, scrolling left or right just duplicates scrolling up or down, and for some reason, scrolling right (zooming out) sometimes stutters. I would have thought that trackpad scrolling was really common now, but maybe it's somewhat Mac-specific?
Agreed, that's annoying. I couldn't find an easy way to separate horizontal scroll event from vertical. But it's something I really want to fix...
The pinch to zoom would work fine, but Safari intercepts this. Modifier key+scrolling to zoom would be fine as well, but not so discoverable. Apple should add some of the iOS multitouch events to Safari, but it's not a good fit since there's really only one visible pointer in OS X. Google Maps would really benefit from this.