I sat next to Paul Syverson at the WESII workshop in Washington DC today.
During a discussion of Firefox/Safari, he remarked that it'd be really neat if something like Tor Button existed for the Safari Web browser (which instead of using its own proxy settings relies upon the OS's settings).
A an hour later, and after a bit if hackery, I present the following:
A script that toggles the proxy settings in Mac OSX (Tiger) on/off for Tor:
As a script and As an application that you can double-click on.
There's also a very useful script available elsewhere which will start Safari in private browsing mode by default.
One item of frustration is that to get any of the scripts to work, you must set the "Enable access for assistive devices" feature in the "Universal Access" system preference. Without this, nothing will work.
This appears to be a reasonably valid security preference in the OS. Without this option, scripts cannot control various elements of the user-interface.