Here is a nice tool for those writing CSS by hand or even using WYSIWYG tools to do it. The CSS optimizer, filters out all unneeded tags (like defining colors twice) and combines things like fonts, backgrounds, borders,… The result should be a better and smaller CSS file, which results in a faster page-load.
I tried it on the version 2 stylesheet of this site and I should change only two things according to the optimizer:
margin: 10px auto 5px auto;to
margin: 10px auto 5px;.
These changes would save me 185 bytes :p. Hey, anything helps.
There is only one downside to it, IMHO, which is that is converts the letters in a hex-value to lowercase.