Twice a day.
Used to be once a day - I need my morning shower to wake up properly.
DW is Japanese, and Japanese people cannot entertain the thought of not showering before bed. So, not wanting to be kicked out of bed, I also shower in the evening now. I turn the water off while I'm scrubbing, lathering, shampooing etc.
It surprises me how many people in the UK apparently shower less than once a day. Or more correctly, it surprised me the first few times I read threads on this topic.