How cold is too cold?

[Aquila]

I can ride down to about 30F, so long as the roads are reasonably dry. Below that, my face hurts, and it's just not fun when my face hurts. But I'm a whuss! Long johns under everything is key for me, and not stopping. I get cold fast if I stop for more than a moment.

[7rider]

It's been said that "there is no bad weather...only bad clothing."
That said...I've ridden when it was 18 F (-7ish C), but it was a short, fairly slow commute and I had on a neoprene face mask. But I didn't really care for it. Tomorrow's forecast says 6 a.m. temp will be 16 F with "feels like" temp of 10! I think I may take Metro in the morning and bail on the bike commute.
Our shop road ride does not officially go off if it's 28 F or colder. Of course, that's probably just the personal threshold of the LBS owner/ride leader, but it seems pretty reasonable to me!
If it's too cold, I'll take care of the errands and chores in the a.m. and ride later in the day when it's had a chance to warm up!