So I had a thought the other week.
How feasible would it be / would there be any interest in running an OpenGrok install for WordPress plugins? Perhaps at something like plugins.opengrok.wordpress.org?
It would make it a lot simpler to check for namespace conflicts with plugins, compatability questions, find usage details for APIs and filters, and it would save a goodly amount of time and hard disk space for anyone currently using @markjaquith‘s WordPress Plugin Directory Slurper (which eats over 4 gigs, takes hours to install, is a nuisance to keep updated, and takes forever to ack/grep through) (but is still far better than any current alternative).
The biggest difficulty that I can see is narrowing it down to scanning only the active branch, since some plugins keep an empty trunk folder, with just a readme.txt to point to the currently released branch. Unless it just scans an install of the slurper being run on an wporg server.