== Mac OS X == 

 There's no mention of setting environment variables on Mac OS X.  While it can be done for the shell, unlike Unix or Linux, the shell variables are not exported when running a GUI application, in which case it needs to be set via environment.plist, as described in http://developer.apple.com/library/mac/#qa/qa1067/_index.html.  I'm tempted to write this myself but I haven't written a long block in such a high-profile Wikipedia page.