Is quantitative easing really helping?

A number of central banks around the world have introduced ‘quantitative easing’ measures to stimulate their economies in the advent of the global financial crisis, with the Bank of England, for example, injecting another £50bn on February 9. They are doing this as they have little room to further lower benchmark interest rates. Does QE represent an essential policy stimulus to get the economy moving? Or is it a ticking time bomb that will lead to a return to runaway inflation?