it has some really interesting concepts built into the language, like time. but in my experience this doesn't provide huge value for the purpose of composition, especially since when you are writing code livecoding is typically loop based.
i'd love a ChucK VM for the web audio API. on the back burner; things i should do but won't.
Then I bought a hefty synth and after about 6 months of sounding like a tramp bashing a trash can lid, I finally clicked and it's an extension of my mind now, much like whistling a tune or tapping one out on your knee with your hand.
Outside of that, you're right -- it's not widely used -- although, at CalArts (where I currently go to college, http://www.calarts.edu), it's extremely popular in the Music Technology department. We use it mainly for handling MIDI->OSC translation to control robotic instruments (http://www.karmetik.com/media) and interfacing other electronics, like custom built musical interfaces and controllers, with music software.
aren't there better tools for MIDI/OSC translation though?