As for myself, I work in a fairly conservative field (life insurance) in a high-level strategic communications role, working directly with the CEO, CMO, etc. Business casual means a coat without a tie, or a tie without a coat.

We have a covered outdoor bike rack, that's the only accommodation for bicycle commuters, but it's enough for my commute. I carry slacks, underwear, undershirt on the bike, change in the restroom so I'm not walking through executive-visible areas in spandex. Dress shirts, ties, shoes, and coat stay at work so I don't have to carry them back and forth on the bike.

I suspect we'd get a lot more bike commuters if we had lockers, showers, etc. As it is, most of the year we have 0.17% bike commute mode share despite being in the Seattle area and having bike lanes right to the office.