Mine's unglazed, and it hasn't been a problem. It's got some blackened bits around the edges, but they don't cause any issue. Sweep a few carbonised crumbs out before each bake. I've never washed it (in a couple of years). From memory I think you're not meant to.
I just bake in tins at the moment but am intending to try a dutch oven, cloche, etc., at some point.
Is it true that they tend to get a bit messed up over time by the act of baking bread i.e. residue tends to get burned on to the surface?