In PHP, this includes methods, constants, and fields inside classes. In particular, I should be able to click on Zerg::rush() and be linked to the definition of the method rush() inside the class Zerg, as opposed to either nothing or a list of all functions anywhere named rush(). (And if I click on $mystery->meat(), it should find all methods called meat(), since it doesn't know what class to look in.) This obviously can be extended to languages other than PHP.
(Aside: It would also be nice to do symbol search on the fly, to avoid having to run a cron job, but I don't think that's feasible. We could at least scan the changed files whenever a new commit comes in, and regenerate symbols for those files immediately.)