I ended up doing it by accident last winter. I had been making consious effort not to use the brake for months, and the one time I did, it stuck shut. There is a brake on my winter bike this year, but I don't know if it's going to stay there or not. I've found that they tend to just fill up with snow.

We finally have ice this year! Some of it is really nasty. The kind of ice where a trail warmed up enough to turn to slush, then people walked/biked through it, then it froze again. That stuff it doesn't matter if you have a brake or not. The bike is going to fall out from under you sideways, and hopefully you'll keep sliding forward from the momentum. Believe it or not, falling and sliding several feet forward on ice seems to hurt less than simply falling on dry pavement...