It's generally just a matter of getting your hands on a .tmLanguage file (the same format as TextMate), and putting it somewhere in your packages directory (~/.Sublime Text 2/Packages/ on Linux).

The top Go.tmLanguage reported by Google appears to be a work in progress though, I'll see if I can get something sorted for the next version - I'd like to have Go support out of the box.

v1 supports custom syntax highlighting definitions (or you could use TextMate's since it uses the same format). I'm sure v2 has this feature also.