A couple of summers ago I painted my sewing room and then got very protective of my walls. I think so far, I only have one nail in the wall -- and that's because I couldn't find a good hook to hang my clock. Anyway, I have several wall hangings on my wall varying in size from 12 x 14 all the way up to 36" square. I've used 3M command strips. I blogged about how I hung my 36" quilt
HERE.
As for my design wall -- it's more 3M strips, hooks and a cheap vinyl tablecloth. I blogged about it
HERE. I've subsequently purchased a larger tablecloth and it covers the entire fireplace wall.