All good points. There's a risk that there's a tilted supply/demand situation. But I think that can be avoided...
I mean there are areas in the world that have both large populations, AND great surf conditions. Think about the US (California, Florida), the UK (Cornwall/Devon/Wales), France (Bordeaux/Biarritz), SA (Cape Town), Austrialia, NZ etc.
And I don't think both parties have to have a surf house for this to work... Think it's more important that both are surfers, so they can share experiences. Maybe a surfer in Hawaii would actually be up for a few weeks in my place in London... or maybe I'm just dreaming....
Anyway, thanks for your comments, think it's worth trying it out at least
