Its great, over 1000 cyclist took part last year. Its an amazing atmosphere. You can do 50k or 30k but I reccomend the 50k as its a much more fun route. There are always a couple of really serious riders at the very front but everyone else is doing it for fun. There are regular cake stops (made by the local villagers, including some of the most fantastic flapjack.) I think I raised about £70 last year + my entrance fee. This year I'm just paying the entrance fee and buying the tshirt because I don't like having to collect sponsership.
I ride it each year with a friend. But my chain snapped last year and I didnt have a chain tool, but a south african guy lent me his but I had to take 2 links out of my chain so I only had about 3 gears for the rest of it.