A while ago, I learned on Unclutterer about a way to separate clean and dirty sponges.
I tried it today and it worked like a charm. The idea is that as your sponge gets dirtier and nastier, you cut off a corner. The more corners that are cut, the dirtier the sponge. So you can use the dirtier sponges for nasty business like cleaning showers and the cleaner sponges for washing dishes.