Jim Glaub's Art Meets Commerce does Internet and social media marketing for Broadway and off-Broadway shows with limited marketing budgets. Word of mouth is already essential to these productions' successes — social media is an extension of that.
Glaub says, "People leave the show and jump onto Twitter to tell their friends how much they liked the show. It's been especially helpful when people with large followings tweet about it, increasing our followers and exposing the show to people that may not have heard of it."
He also reports that celebrities will attend the shows and tweet about them, providing even more exposure. Having an active Twitter presence encourages these theater fans to spread the word and encourage their own followers to start tracking the show.
For small business owners, it is important to remember that some people will tweet about you or review you on Yelp whether you have a presence there or not, and what they say might not be positive. You need to be on the ground, ready to deal constructively with any negative exposure. As stated previously, you should be participating in and guiding a two-way conversation.