But, their public code search was not the same as the internal thing, as far as I know. The internal beast sounds kind of awesome. Here's his talk about it from a few years ago: https://www.youtube.com/watch?v=KTJs-0EInW8

I think the really useful thing (beyond a mere search engine that has indexed a lot of source code) is the comprehension of the "guzzintas" and "guzzouttas" of the code, more than merely a naive word search; i.e. knowing how pieces interact, so you can search for functions that work with a particular kind of object, for example, or objects that have the same properties, or code that interacts with the same API you're working with, whatever.