I'm lucky enough to have a shower at work and with the way I sweat (sorry) without them I wouldn't be able to cycle. When our showers were closed as part of the anthrax decomtamination process I wasn't able to cycle for 3 months (I suppose I could have taken out a 'showers only' gym membership but was too cheap).
I'm also lucky enough to have a casual dress workplace so I generally just leave a couple of pairs of chinos and a couple of polo shirts at work.
on summer days I'm probably cleaner and fresher than everyone else because they have to walk from metro/car to the office in 90+ degrees while I'm showering in the office!