I play at my local Borders sometimes (I have a performance scheduled for Sunday). In my experience the audience applauds but they're not inebriated, they know people are also in there browsing and reading, and as several pointed out it is a very laid back atmosphere. There isn't any danger of them applauding so furiously that they will disturb the whole bookstore - at least I've never provoked such a response! I love playing at bookstores. The audience is more sensitive, educated, appreciative and I can do a lot of songs that would never be appreciated in a pub.