I can't find the link now, but recently Mo Bike Fed had a survey called "Are you a winter cyclist?" There were 2 questions. 1) What is the lowest temperature you are comfortable biking in? 2) How many times have you cycled in the past month?

The answers were all-or-none. Either 40F, or no lower limit for lowest temp. Either too many to count, or not at all for number of times on your bike in the last month.