Absolutely loving this! Much like a breath controller, it adds a level of expressive capabilities that you just don't have with wheels, joysticks, pedals and the like, bringing the synth/sound design experience another step closer to "real" instruments.
What inspired me to investigate alternative MIDI controllers is my picking up the violin and cello a few years ago, and a growing desire for more expressive freedom with virtual instruments and synths as well. I believe there is a level of musicality that can only be explored and developed with instruments that instantly respond to subtle details of your playing - but I don't see why we can't have that with electronic instruments as well!
The output from this controller near-audio-rate, and it's fast and sensitive enough that you can use various finger tapping and sliding techniques on it, making it feel and respond almost like the skin of a drum. I'm not quite sure how to apply this to "traditional" synth presets, but for those of us programming our own sounds, it opens up a another level of expressive possibilities, much closer to acoustic instruments.
Downside: After trying this, you might be tempted to pre-order the Osmose.