Helicopters, while very capable and versatile aircraft, aren't known for high speeds. Even a recently released twin engine Bell 429 (http://en.wikipedia.org/wiki/Bell_429} cruises at "only" 150 knots. Yes, faster than the Cessna 172 four seater I fly, but slower than many other light single engine planes. Enter the Sikorsky X2. Still in prototype stage it's already reached 181 knots and is destined to cruise at 250 knots. Sikorsky uses counter rotating blades for increased efficiency at high speeds (as well as overall stability) and a pusher prop to give it that extra "oomph" :-)
Why focus on 250 knots? Because that's the FAA mandated maximum speed for aircraft under 10,000ft. It came about after this accident: http://en.wikipedia.org/wiki/TWA_Flight_553.
More details on the X2's flight: http://www.aopa.org/aircraft/articles/2010/100607sikorsky.html