Livemarks. Watch Del.icio.us live.
Web 2.0 overload - "eHub is a constantly updated list of web applications, services, resources, blogs or sites with a focus on next generation web (web 2.0), social software, blogging, Ajax, Ruby on Rails, location mapping, open source, folksonomy, design and digital media sharing." Tons of links to mashup apps like PervWatch, Podomatic, ThinkFree, etc, etc, etc...(note: a lot of these sites are in beta)
You've heard of Greasemonkey (which allows you to remix web pages in firefox), you might also remember the Ruby Programming Language that all of the cool kids are talking about these days. Mix the two together, make it useable through any modern browser (using a proxy), and voila MouseHole!