How long does it take to get to Pluto?

It would take several years with current technology, much longer if there were constraints on the amount of available fuel, because this determines the trajectory to be used.

The New Horizons project (see link) uses planetary gravity assists to reduce the travel time. It was launched in January 2006 and should arrive near Pluto in July 2015, "only" a 9-year voyage. That will be our first close-up encounter with the dwarf planets Pluto/Charon. The spacecraft will not actually slow down to orbit Pluto, but rather make a rapid fly-by.

You could reduce the travel time if you had really big engines and could simply boost all the way there. You would need big engines coupled with modified solar sails assisted by giant earth-based lasers. Given unlimited fuel for acceleration, Pluto could be reached, one-way, in a year or two.

Most trajectories take braking into consideration for orbital insertion. Whatever time you spend accelerating, you must spend an equal amount of time with your spacecraft turned the opposite direction, main thrusters firing to decelerate. Trip times are reduced by burning more fuel at each end. Most trips through space consist of an initial boost, lots of coasting, and a final decelerating burn towards arrival. When you think about it, automobiles and passenger trains travel the same way. The car or train accelerates on leaving the station, travels a long way at a constant rate, then decelerates to stop at the destination.