There is this great myth that a marketer is critical for start ups. However, all the marketing you need for web apps is to verify that there is a serious problem that you can solve/alleviate. If you build something truly useful with a specific group in mind, then marketing will be easy. When people's hair is on fire, and you're the only one with a fire extinguisher, it's not going to be a hard sell. IMO, most hackers have trouble identifying and solving a worthwhile problem.

For your specific application, social networking for climbers, is there really that much of an interest? Is this something that climbers want? Will you be able to compete with Facebook?