Check out this post I just found on café writing here.​ Nice to hear someone discussing the rituals and etiquette of writing in cafés, even if it has taken me over a year to find this particular blog entry!  I also hadn't heard of David Mamet's book 'Writing in Restaurants'. Guess I am behind the times: it was first published in 1987. Oh well! Better late than never. Sounds like it doesn't have much to say about the act of writing in restaurants, at any rate: nevertheless, I will check it out.