Perfect is in the eyes of the beholder. Even though Seth is talking about a billboard in Grand Central, many of businesses with websites will be stumbling and chocking on "perfect" Greasemonky scripts.
Using Greasemonkey, "The idea of embedding an application in my current (and transient) context is very powerful" from Infectious Greed, which led me to a post from Nive "Greasemonkey will blow up business models (as well as your mind) that really demonstrates the power of GW scripts and the effects they will have on businesses. Anybody with a website has to be looking at and learning this stuff or their business will be toast.
As Nive mentions in his post, it's about the "api's". Amazons' got'em. I haven't seen too many other businesses that will be able to leverage Greasemonkey in their favor. They're fucked. What's so tragic here is that those affected businesses will most likely do the dumbest thing - develop a strategy to fight against GW scripts and screw things up for their customers/users instead of learning how to work with them.
Talk to me.