I had a very good commute this morning. First time I break some real sweat on my commute for a very long time. There was a foot of wet snow on the bikepath that made the day very interresting, to say the least. I ride on knobbies now, and with the normal 65 psi the tyres cut through the snow, the rear wheel was spinning and I had some serious gravity-problems. But after I let out the almost all the air from the tyres I had some flotation, good control and managed up to 8 mph on the flats.
After I got from this bikepath and on to the streets I sure had good traction, but the rolling resistance was immense. I think my max speed today was around 12 mph.