When I first read the patent, I thought that it was technically infeasible to detect 3D hand gestures with ultrasound waves. But I soon realized that there are plenty of medical imaging devices using ultrasound. Good idea and good patent.
In addition, I guess that Elliptic Labs 3D touch sensing interface also uses that kind of ultrasond imaging technique.
Updated Dec. 11, 2009
US20080005703 Apparatus, Methods and computer program products providing finger-based and hand-based gesture commands for portable electronic device applications -