Apple's QuickTime hub includes multiple "TV" channels, streaming news headlines, and a free downloadable player that brings it all together for a clean broadband experience.
Although it's entertainment oriented and not for the faint of heart, Heavy.com is a good example of interface design that makes use of broadband technologies. Very dependent on the Flash plug-in.
A hugely-active broadband visual community coded in Macromedia Shockwave. An incredibly immersive (and addictive) environment that shucks all Web conventions quite successfully.
Search for Extraterrestrial Intelligence at Home, the most well-known example of processor sharing.