The error 'command not found' means that the command is not found in the $PATH environment variable.

If you installed blender as described in the [Wiki Installing Blender on Mac](http://wiki.blender.org/index.php/Doc:2.6/Manual/Introduction/Installing_Blender/Mac). The executable `blender` is located in /Applications/Blender/blender.app/Contents/MacOS

You could simply open your terminal and enter

    cd /Applications/Blender/blender.app/Contents/MacOS
    ./blender 




    ndof: 3Dx driver not found
    found bundled python: /Applications/Blender/blender.app/Contents/MacOS/2.68/python


This answer is incomplete since I couldn't manage to add the directory `/Applications/Blender/blender.app/Contents/MacOS` to the PATH variable in order to launch blender from everywhere. 
Unfortunatly the [Docs](http://wiki.blender.org/index.php/Doc:2.6/Manual/Interface/Window_system/Console_window) don't cover this topic.