How many threads have you read that people have not had any problems? I have never been asked to leave a store, I have been asked to cover up, but it was by a worker bee not managment and I told them I did not have to, and they said ok and left. I have never sent a written warning that I am looking to openly carry in their establishment. I figure I will carry and if it ever arises then I will fire off 1 letter to find out about their policy. Given a forwarning and a chance to create a policy where one was not in place, I dont think is a good thing to do, especially if someone else has been carrying at a particular establishment and now more attention will be brought to them. That is just my opinion, to me it's like peeking into a store and asking the clerk if it's OK to open carry there, before you walk all the way in.
If you do, be sure to keep us posted on your results and send any written responses to M1gunner so he can post them on his policy page.