Most of mine (and certainly all that I make from work) are in my lunch-break, so I'm not sure that would tell us anything. To be honest I really don't know why "time spent on this website inhibits productivity" was mentioned as being related to cycle-commuting. The only difference with non-commuters here would be time spent on different websites.

In answer to the original question, I rarely (if ever) have sick days, so I'd say it's a plus from that perspective. However, I rarely (if ever) work overtime either, simply because I want to get started on my ride home. I suppose one advantage is that I'm never "stuck in traffic" either.

I think there's more to making a productive employee than the mode of travel they choose to get to the office.