Generally speaking, I'll ride unless I think the wind may knock me over. That hasn't actually happened yet, but once it's a little over 30 MPH it seems to get close and the ride can be a little skittish at times. If I'm going to be on snow and especially ice I'm a little more cautious and would probably drive if the winds were much over 20 MPH. I'll often ride just the last quarter of my commute, around 1.7 mi and safer, if I read about 40-50 MPH gusts, but even then I haven't been knocked down. I take direction into account too.

As someone else said, in windier conditions I'd probably prefer my heavier bike (my Swobo Dixon) instead of my road bike, but I'm not convinced it makes much difference. Anyone care to elaborate on this point?