I don't use snow tires in the winter. There might be 5 days out of the year I really need them. It dosen't seem needed for the whole winter. But I do take my tire pressure down. I thing it helps with grip. I remember last winter driving in the snow with 45psi being very slippery.
2008 EPA adjusted:
Distance traveled by bicycle in 2007= 1,830ish miles
Average commute speed=25mph (yes, that's in a car)
I have a set of mounted snow tires that are generally on from December until the snow quits flying. All seasons are OK most of the time but I would rather be safe than sorry. Well worth the money for the extra safety margin IMO.
Most all-seasons will get you by OK, providing they're in good condition.
One caveat to that, is if the vehicle purchased came with "Summer Only" Tires.
In the following example, summer tires wouldn't have yielded this kind of traction:
I still miss those days, but how often can you do that in KC? Twice a year, if you're lucky. I still have the half-worn summer tires (Yokohama Advans) than I've been trying to give away, but they don't fit many rims!
My set of winter boots / rims are currently on the ForkenSwift. I didn't mount them on the Blackfly last winter and missed having them (the OEM LRR Invictas absolutely suck in slippery stuff).
However the snows are a size shorter and wider than the Blackfly's OEM tire (I know, that's not the way to size a snow tire, but it was a sale tire closest to my size, and I wanted them NOW). So in addition to losing the LRR benefit when I put them on in a month or so, my FE is also going to be taking a hit from the effective gearing change and slightly worse aero.
Hmm! This thread prompted me to figure out my outside tire diameter with the 2 tires, and they're actually not that different - my snows are actually only .5% smaller OD than the stock tires (though they're 20mm wider).