I was there when we added it to Preview ;) I think Nils wrote the code to hook it up, because he also worked on the loupe and how it would automatically lock onto the bounding box of a line.
Hi, Matt. Yeah, one of the engineers is on HN from time to time — I thought he might see the post and respond. (Your reminding me of Nils made me smile this morning.)
Ahem. Actually what I am most proud of is that I made pinch to zoom keep characters focussed during zooming. At that time, Safari let things get blurry until the user stopped zooming and then it snapped to focus. That is what I was supposed to do, but I decided to use mipmaps instead.