B Mode and Winter Weather

In general, I don't think it would help much.

However, in one specific instance, I know it helps a lot...

There have been many times when I've encountered slushy/icy roads that are so slippery that you have to creep (like 5 MPH) down steep hills and even the slightest touch of the brakes puts the car in a skid. I have found that in such circumstances, putting the Prius into "B" works much better than trying to ride the brakes, because it keeps your speed down with gentle, consistent resistance, where as with the brakes you have to keep varying it and with the slighest overpressure on the brake pedal starts you skidding.

So don't bother with "B" when you are just tooling around at 20-30 MPH in the snow. However, definitely use it down hills that are so slippery that even 5 MPH seems harrowing.

 

Driving in B-mode (ie accelerating) doesn't get you any benifit. Instead, B-mode helps you to slow down by transmitting some of the energy from the wheels into running the engine (bleeding off the energy, as it were). As you said, your mileage will take a hit driving around in B. But you won't get any handling improvements. Like Marlin suggested, there may be one or two situations where you might use B-mode in the snow to help prevent skidding, but those are probably few and far between.

B-mode does nothing to help increase control other than bleed off energy - so slamming on the brakes suddenly or turning the wheel sharply will still put you in a skid regardless if you're in B-mode or not.