CSS optimization tools
The aim of any CSS optimization tool is to reduce the size of the CSS file by reducing whitespace, shortening style rules, and removing extraneous properties. The result should be a decrease in page download times (although you will not notice this on a broadband connection) and bandwidth savings.
The tools reduced the size of the CSS file by up to 69% in 24 different tests. However, I was struck by the number of failed tests (9 of 24) where the 'optimization' caused CSS display problems. Not so great.
The best of the CSS optimizations tools was Icey's CSS Compressor which produced some impressive reductions in stylesheet size. However, even it failed the test on one stylesheet.
Overall, I'd still be worried by the failure rate. If you are going to optimize your CSS with tools like these, use with caution would be my advice.