I generally Powerwash my equiptment once a month, and scrape the grass off inbetween those times. My advice is run the blades on pavement for a little while to dry off the deck, use towel to wipe excess water from on top of deck, and fill the spindles with grease before you power wash, so there will be less of a chance of getting water in the spindles.
I power wash my equipment occasionally and only when extremely dirty. I make sure I never blast the water at the spindles, bearings or electrical parts or controls. I always make sure I grease AFTER I'm done washing to squirt out any water that found its way in somewhere it shouldn't be. just don't get too carried away and you should be fine.
I know Toro just suggests washing their equipment with a regular garden hose. If you blow off the equipment at the end of each day it keeps the mess to a minimum. Then if you wash with soap & water from a garden hose once a month of so it will stay looking pretty good. Might also want to apply some wax after you've washed it.