Last fall (after starting this thread) I borrowed my friend's pressure washer for the haulout, and after using it I could not imagine not using one to clean the slime off the bottom. A fresh coat of bottom paint this spring has failed to stop the slime, so I'll need a pressure washer again for the bottom, as well as some projects around the house. I've borrowed one so many times that I figured it's time to get my own.
I followed the advice provided here to get the most powerful one that is practical to store and transport, so I picked this up on sale for $360 at Sears last Sunday:
I still have not had time to get it out of the box, but hoping it works reliably.