As an unnatached runner myself, I take exception to some of the posts on here...
There are many reasons why someone would want to be an unnatached runner - it aint the cost of joining a club, as I'd save more on (road) race fees than it costs to join most clubs!
I actaully once won 1st Unnatched runner prize in a local road race. Whilst I was chuffed to get my first prize, I did query with the organiser (a friend) why I deserved a prize when I was only 25th. His answer was that as an unnatached runner, you don't have the network of support that a club runner usually has, and so in some ways its harder to reach a particular level. Although I see his point (to some extent) for local club based road races, I don't think the same should apply to fell races. For me, road races are all about pace, and structured training is key to being fast, but fell races are more a labour of love and I don't think the benefits of being in a formal club are so distinct.
Still depends on the club, and also personal comitment?
Success is the ability to go from one failure to another with no loss of enthusiasm.