I average about 12 or 13 per year. Usually by stewarding. Its great fun and you get to see people (bands etc) whom you may not go to see if you had the choice but actually enjoy, once you are there (if you see what I mean). This is how we met Hissyfit at Saddleworth and recommended that they came to Cleckheaton for the 2007 festival.
Meeting other festivalgoers is fun too. The folk festival scene is one big happy family, usually.