I've had a pro since it came out and I do not use a screen protector. There are no marks on the glass. On my galaxy nexus 10, I do use a screen protector but do not like it for it has a lot of small marks that appear permanent in the soft protector. The protector also slightly degrades the touch screen in the nexus. I too would like to here a pro owner who uses one.
I'm using the Incipio self-healing protector. Works great with the pen. Collects fingerprints less than I'm used to other screen protectors doing too. So far I've been very happy with it. So much so that I wanted to get one for my phone but they don't make the self-healing one for that.
I ended up buying an incipio but they wouldn't put it on for me (I guess if they ruin it then the consumer might want another one) so I will have to be careful until my friend is able to put it on for me. (Am absolutely hopeless at doing it)