Car in this weather nowadays. I've done my bit of riding in all weathers, rigmarole of pulling all the gear on, then taking it all off again at work, finding somewhere for it to dry, then doing it all again to go home - only 3 miles to work for me, on a little country lane, so doesn't seem worth it for that. Bike barely warms up in that distance. Plus, these days I don't care to be having to keep on top of all the cleaning and winter maintenance it requires. Keep it on the road through winter tho, cos of those nice sunny, dry days you get now and again. Never know when the mood might take me!
If I could afford a winter hack, on the other hand, I'd probably bike it much more often.