I though that only the 17" MBP came with this feature. On other models you have to use a hack to enable it, basically just use the pref panel that comes with the 17" MPB OS X built, however it resets when restarting and you have to re-anable it from the mouse & keyboard prefs. My guess is that its gonna be enabled for all computers with the 10.4.7 update since its just software.