At the start of the rainy season (now). I switch over two weeks ago and was glad to have the winter tires on the Impreza with an unexpected trip to Cashmere yesterday. Stevens was bare and dry on the way out, but slightly covered with a light dusting on the way back in the afternoon
I'm a firm believer in studless tires. The noise and road wear isn't worth the extra cost of the studs. And I personally believe studless is better anyway.