About Debian Code Search
Debian Code Search (DCS) is a search engine for source code — it searches all the open source projects which are included in the Debian archive (the "main" distribution only, not non-free or contrib). Currently, that includes about 18000 packages with 140 GiB of source code.
DCS is the subject of Michael Stapelberg’s computer science bachelor thesis (1 MiB PDF).
There also is a 50 minute talk about DCS which you can watch at http://www.youtube.com/watch?v=n6DtW3zCTvk (with English subtitles).
-- Michael Stapelberg, 2012-10-02