Code Access Security and Bitfrost -- can Code Access security be made usable enough to work?
Wonder of the When-Be-Splat -- very nice compact Ruby idiom
Higher-order Messaging -- a the next logical step after higher-order functions
Cross-browser scripting with importNode() -- abstracting away browser dependencies for AJAX style applications
Software Development as a Collaborative Game -- remembering the fun
Software Projects as Rock Climbing -- that sort of collaborative game
Machine tags and ISBNs -- interesting application of folksonomy