to Chow,
yesterday i found a solution that we can have system wide ErgoEmacs keybinding on the mac.
The trick is to use mac os x's keybinding system so that you have system wide ErgoEmacs keybinding with the Control key. Then, in OS preference, swap the Control and Cmd key.
So that, you get ErgoEmacs keybinding system wide with the modifier beside the space bar. The draw back is of course that normal mac Cmd+key is now at the corner of keyboard. So, it's a trade off, about whether you use most apps for text editing, or the app's shortcuts.
might give it a shot here:
http://code.google.com/p/ergoemacs/wiki/ErgoEmacs_keys_system_wide
also, few years back i tried the mac's os wide custome keybinding, some cocoa apps still doesn't support it. See bottom here
• How To Create Keybinding In Mac OS X
but perhaps things are better now.