Text Expander on Mac OS X

I'm assuming you're talking about the Language & Text > Use symbol and text substitution option found in the System Preferences.

Per comment on Tuaw: Set up Mountain Lion's text expansion options

It does work - at least in most native applications - but you need to turn it on in each application. Per Apple Support: Turn on text substitution features in an applications. Control-click and choose Substitutions > Show Substitutions. (In some applications, you can also choose Edit > Substitutions > Show Substitutions.) In the Substitutions window, select the text substitution features you want to turn on.