If there is one thing Mac OS X is lacking is a suite of tools for measuring usability metrics:
DeskScribe is a (GNOME) suite of tools for recording a user’s desktop activity in usability testing scenarios. Currently, it only captures and logs mouse activity data. The log format is completely compatibile with that of LogSquare. There is a huge TODO list for the project, but currently we can log mouse data, and render activity graphs from that data, in the Mausgrapher application that is included in DeskScribe.