Another reader suggested a helmet would offer protection from flying skis when a skier takes a "ski sale" kind of fall. I don't dispute that point of view, either. And certainly, a hard-shell helmet provides a more windproof and probably warmer way to cover your head, particularly in very cold conditions.
That said, I still don't think your average skier needs to rush out and plunk down $100 for a helmet. Yes, head bangs certainly occur on the slopes, but in contrast with activities such as bicycling or rock/mountain climbing, I'm not sure helmets confer an exceedingly real benefit to the recreational skier. Speaking personally, in all the years I've been skiingand fallingI've never really felt that a helmet would have been of much value in this situation or that. Helmets when biking and climbing, though, have been called into action lots of times.
Generally, a common-sense approach is best. I think everyone just needs to make a judgment based on his or her own comfort level, the ski conditions and terrain, and what seems to make sense.