I recommend a screen protector. I used a JAVOscreen with my Treo 650 and I bought an N800 JAVOscreen protector for my N900 and cut it down to size. It's a great thing to have, you just don't have to worry about scratches *at all* (at least not on the screen area, this protector only covers the screen plus a little extra space on the sides.) I haven't had any problems with it getting dirty or anything, just set and forget. My experience with other screen protectors has been pretty poor though.
