I keep mentioning Greasemonkey but haven't yet had a chance to write up why I think it's important. Luckily I keep running across others who are doing a pretty good job. Ryan's Greasemonkey Stole Your Job (and Your Business Model) is one such example. It's where I learned that a trivial Greasemonkey script exists for blocking AdSense Ads (actually it just hides them). Scary stuff, huh? :-) He spec