If you use Xcode, it's extremely useful to have your header files indexed by Spotlight. This isn't done by default, and it isn't well documented how to achieve it.
It's actually pretty easyl. Open Terminal, and then run the following three commands:
$ mdimport -f /usr/include
$ mdimport -f /usr/local/include
$ mdimport -f /System/Library/Frameworks
Spotlight will then index all of the header files...
Mac OS X Hints
http://hints.macworld.com/article.php?story=2005102909155046