Today, I have uploaded my second Greasemonkey scripts to userscripts, Yahoo webmail++ . This will remove (hide) the advertisements in your yahoo webmail, the one at the top and the small ads on the left side.
Ok. My first Greasemonkey script is available from userscripts.org (http://userscripts-mirror.org/scripts/show/9740)
I have been using Greasemonkey for more than a year. Recently I downloaded 2 userscript, GMail superclean and Gmail air, which inspired me to write a script.