Do I wash down my bike? NO!
Here are a few pics of my bike after riding all winter in mud/rain/snow/slush/sand/salt
That is a mixture of grease, chain oil, dirt, sand, and salt on the BB area.
Spring is my bike wash. When things get wet around here, my bike will be washed for me.
Interesting little tidbit about the clip on rear fender that I have. It seems to funnel water/snpw/grit/etc. towards the BB junction. It never got this dirty last year, or any of the other years that I have had the bike.