I've seen the same woman commuting over the past year along my route. I've seen her and one other guy commuting regularly by bike. So, I guess that makes it 50/50 in my limited experience.

Counting only those who commute where I work it's 100% men who commute by bike. Me and one other guy...that's pretty much it. Quite a limited sampling I'm afraid. I don't think you could draw any conclusions from it...sorry 'bout that.