If it's in Photoshop and it goes fast, there's a very good chance that Chris Cox has had something to do with it.  Chris is, among a great many other things, the go-to guy for optimizing many functions in the app.  (At various times we've known there's some kind of crazy-exotic Apple hardware in Chris's office--something that would emerge many months later as the G5, etc.--and that he's busily tuning the app for it but can't tell us any of the details.)  In any case, he has started a blog on C++ performance.  If that's up your alley, I recommend subscribing to the feed.

[Semi-irrelevant personal aside: After so many years of consulting Chris to learn about HDR imaging, color management, GPUs vs. CPUs, and so on, I'm taking some pleasure in sharing my meager (yet superior) knowledge of CSS with him, hipping him to groovy tools like Xyle scope.  I've gotta enjoy the moment while it lasts!]