This, as an offshoot of robotics, is one of my personal deep and abiding interests :)
By far the biggest problem with the system is the power supply... carrying the power needed to power the suit for any reasonable length of time would negate any benefit the suit offers :(
This is (one of the reasons) why I'm also so interested in electric cars, such as the Tesla Roadster (as my current favourite). Car industry investment in better battery tech might be exactly what the planet needs :)