ION Drive technology for earth bound transportation?

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I have an intense interest in the possibility of combing ION drive technology with earth bound modes of transportation. I was searching the web for information regarding rail guns or electromagnetic propulsion and came across this article: http://www.sandia.gov/media/newsrel/NR2001/flyer.htm In this article they state that the Z accelerator machine they have is propelling a dime sized pellet called a flyer plate to a speed of 20 km/sec- almost 3 times the speed needed to escape the earth's gravity of~7 km/sec. A rifle bullet is roughly 1 km/sec. On the NASA website for Deep Space 1 at: http://nmp.nasa.gov/ds1/tech/ionpropfaq.htm They state that the Xenon gas which is electrostaticly sped up upon exit from the ION drive, reaches a speed of 30 km/sec. Now my question is, why is this not a viable form of propulsion on earth? Is the Xenon gas not a heavy enough molecule to cause actual propulsion when gravity, drag, and other forces are taken into account?I can't get past the idea that this could be integrated with another technology to be suitable for vehicles and human transport.