This is an example what happens with your CSS code if you feed CSSTidy with it (default settings and ver. 1.0beta).
The stylesheet I used comes from from sourceforge.net and is 23.2% smaller after optimisation (although the optimised version has a higher readability). See yourself.
Another example is taken from xhtmlforum.de and can be compressed by 38,3%. The maximum compression achieves 46.2% here.