Greasemonkey
Ryan Shaw: The key to survival will be going meta: design for the bright kids. Create a flexible, modular set of APIs and a well-documented example UI or two that shows how they are used. Learn from Amazon and release your grip on the end-user experience. But developments like Greasemonkey disrupt more that just job descriptions: they disrupt business models too.
Here’s a directory of scripts. For Safari users, check out PithHelmet Machete scripts.
My favorite example so far is Simon Willison’s msdn-platinfo.