IMHO, taking people’s wash out of the machine and stacking it somewhere is not a breach of etiquette. The other person should have been there to take it out themself. If you relinquish that responsibility don’t be getting upset when someone does it for you. And don’t dump a used litter box into the washing machine.
Also, taking stuff out of the dryer is appropriate too. Really, really nice people will fold it for you.
Not So Fast 
I am going to pass this along to Peanut, Marmitetoasty’s matie, because her last post on her blog–accessed through Marmitetoasty’s blog–touched on this subject.