I know what you're probably thinking. Cheesy video game soundtracks on your SoundBlaster sound card. Web pages with blink tags and bad music tracks on autoplay. They represent one use case where MIDI was applied outside of its original intent. MIDI was made for connecting electronic musical instruments, and it is still very much alive and well. From lighting control systems to professional recording studios to GarageBand, MIDI is a key component of arts performance and production. MIDI connects sequencers, hardware, software synthesizers and drum machines to create the music many people listen to everyday. The specification, though aging, shows no signs of going away anytime soon. It's simple and effective and well crafted.
There's been a lot of interest and some amazing demos of Web Audio API functionality. The Web MIDI API, on the other hand, hasn't gotten much support. Support for Web MIDI has landed in Chrome Canary, but that's it for now. A few people have begun to look at the possibility of adding support for it in Firefox. Until the Web MIDI API is widely supported, interested people will have to make due with the JazzSoft midi plugin and Chris Wilson's Web MIDI API shim.
I remain hopeful that support for this API will grow, because it will open up doors for some truly great new creative and artistic initiatives.