I have revisited adding Yui compressor into my work's ant build script to minify JS and CSS scripts. The current jar was yuicompressor-2.3.5.jar . It took a lot of playing around but I finally stumbled on how to get it to work. Here is the snippet for the yuicompressor. I had to jump through a couple hoops like overriding the current js/css scripts with the optimized js/css scripts. I'll release a full working copy in a zip, you can run against your webroot. We achieved an average 18% compression rate for all our js/css files.

UPDATED: ADDED ZIP EXAMPLE

Orginal Post: Adding JS/CSS compression and JS validation using YUI Compressor, JSLint, and jsmin to ant script

<!—
minify
Now minifying js and css files
—>
<target name="minify" depends="exportCode" description="Now minifying js and css files">

<echo>
Now minifying js and css files
</echo>

<apply executable="java" parallel="false" dest="${webroot}${temp.dir}${jarfileTstamp}">
<fileset dir="${temp.dir}${jarfileTstamp}" includes="**/*.js" />
<arg line="-jar"/>
<arg path="${webroot}libyuicompressor-2.3.5.jar" />
<arg line="-v"/>
<srcfile/>
<arg line="-o"/>
<mapper type="glob" from="*.js" to="*-min.js"/>
<targetfile/>
</apply>

<move todir="${webroot}${temp.dir}/${jarfileTstamp}" overwrite="true">
<fileset dir="${webroot}${temp.dir}${jarfileTstamp}" />
<mapper type="glob" from="*-min.js" to="*.js"/>
</move>

<apply executable="java" parallel="false" dest="${webroot}${temp.dir}${jarfileTstamp}">
<fileset dir="${webroot}${temp.dir}${jarfileTstamp}" includes="**/*.css" />
<arg line="-jar"/>
<arg path="${webroot}libyuicompressor-2.3.5.jar" />
<arg line="-v"/>
<srcfile/>
<arg line="-o"/>
<mapper type="glob" from="*.css" to="*-min.css"/>
<targetfile/>
</apply>

<move todir="${webroot}${temp.dir}/${jarfileTstamp}" overwrite="true" >
<fileset dir="${webroot}${temp.dir}${jarfileTstamp}" />
<mapper type="glob" from="*-min.css" to="*.css"/>
</move>
</target>

Minify CSS/JS ant revisited using YUI compressor