We put studded snow tires on it and there wasn't a day this winter that my wife didn't drive it into Burlington into work. I think she would still prefer to drive our Honda Civic in the winter, but it did the trick.
The people who complain about the Prius and winter driving are most concerend about its Traction Control System, which primarily exists to not allow the driver to spin the tires so fast that it will burn out the electric motor. People have complained about the traction control system shutting down power to all wheels when going up snowy/icy hills. In most case those complaints are coming from people without snow tires on the car. Snow tires seem to alleviate most of the problem.
You can get a lot of information at
www.priuschat.com