Groupon and similar sites like Tippr, Social Buy, and Living Social are great sites to find a deal and they can get the name of your salon into the email inboxes of many potential new clients. However before signing up to sell your services at a heavily discounted price you should consider the type of potential clients that this may be bringing you.
Social buy sites are becoming very popular but they have also been around long enough now that they have generated their own customer following. In other words you are running the risk of just selling a large amount of work for yourself with little to no client retention. The reason for this is that you are selling services to the social buy site's customers. People who have signed up to get the latest deals. They don't necessarily care about how great of services you provide because they are there for the price only. And their next hair service will be with the next salon on Groupon offering a deal.
This article on cnn.com, "Groupon study looks at culture of cheapskates" makes a really great point.