At $180, and the fact that it only works with the iPhone also factors into it. I think the problem is that it's not good enough for most pros, but it's probably too expensive for the casual user.
NotesOnVideo: Shooting with the iPhone 4
NotesOnVideo: Steadicam Smoothee Unboxing & Initial Impressions
B & H: Steadicam Smoothee for iPhone 4 [$179.95]
Amazon: Steadicam Smoothee for iPhone 3GS [$179.95]
B & H: Steadicam Flip Ultra Smoothee Mount [$24.95] - not yet shipping