Deep Space One was flown by NASA as a test bed which included proving the Ion Engine and the Japanese currently have Hayabusa on it’s return trip to Earth, hopefully with some asteroid soil samples. ESA flew one last year on a moon mission and in addition to those missions there are several ion engines performing on Earth satellites as station keeping thrusters.
Over a year ago I read an article about some Australian engineers and scientists who had developed a new ion thruster 10 times as efficient as the ones currently in use. Four times the thrust too.
http://en.wikipedia.org/wiki/Deep_Space_1
http://en.wikipedia.org/wiki/Hayabusa
The Hyabusa ship has been lost and recovered several times. It should have disappeared a couple years ago, but the engineers have somehow kept it going. It wasn’t going to be possible to return to earth, but here it comes. This is a story of the impossible and would be dramatic if it weren’t happening so slowly and so far from earth and just a robot.