I've been driving T4R's since 1990 and lived in PA up until 2 1/2 years ago. I've recently moved to the Chicago area, so howdy neighbor!
I prefer to leave the 4Runner in 2WD until such time that really feel that I'm having problems. By doing this, I feel that I maintain some of my 2WD foul weather skills in lieu of relying on the car to do my driving for me. The problem with the newer 4Runners is the Traction Control System. When it kicks it, you lose some of the control over the vehicle that you need so I'll turn it off under selective conditions.
I think relying on 4WD all the time increases our dependence on it and we suffer in the long run by forgetting how to DRIVE the car in bad weather vs. letting it take you for the ride.
As a side note, it you have the Dumbflop Grandcrap AT20 tires on the car, they're barely marginal in snow. If you have the cash, I suggest a better tire. The Dunlop is ok as long as you're very gentle but in all honestly and from past experience with tires like the Firestone Destination LT and AT, Michelin LTX, Bridgestone Revo and a few others, the peace-of-mind with a good tire is worth the $$.