Do I ride when ill? Sometimes yes, sometimes no. I can't remember if I've ever taken a full day off from work for illness (gone home early a couple of times), but then my work is mostly of the mind and not physical (unless you consider math and programming to be physical, heh). I've finally come to accept that at least in the winter, it takes me longer to get to work by bike than by subway (from prep / dress time to ride time) so I'll get more sleep if I don't ride, and sleep is very important when sick.