Recently some physicist have observed electrons having a negative mass before undergoing acceleration which is more or less what woodward expected which means that his theoretical mach reaction-less propulsion device might just be possible, but you would still have to power the thing and scale up it performance to meaningful levels.
various people are studying the mach drive and some have reported limited success, work is still ongoing.
electron negative inertial mass
http://www.sciencedaily.com/releases/2010/04/100412084525.htm
http://www.technobahn.com/news/Negative_Mass_and_High_Speed:_How_Electrons_Go_Their_Own_Ways_2010041200003007.html
woodward mach drive
http://www.centauri-dreams.org/?p=1324
http://en.wikipedia.org/wiki/Woodward_effect