They sent out a Myspace message (login req.) to all their friends (i.e. people who have given them permission) saying:
Get free entrance to The Independent Armchair Theatre by reviewing the next show you go to.
All you have to do is post a review in our Myspace comments section. This will get you 1 x free entry. The next time you arrive at The Armchair your name will be on the guest list.
Your review then gets posted on their website - so they get lots of reviews for free, while also attracting opinion leaders (who care enough to write reviews) for a follow-up show. The reviews get republished on their main website to give the reviews even further reach... Effectively Turning Customers Into Evangelists (<< click if you didn't get the obscure reference to a funnel in the title of this post).