I think that its hard to just pitch a idea to somebody else...its all left to their imagination. Better to have already a prototype or something and have people play with that. The feedback will be much more valuable, then just shooting out some draft idea over a beer...you know what I mean!?
It took us about 10 months to get there. I don't have a graph handy but it was pretty linear from month 4 onwards. Before that, we had an accelerating curve because we started at 0 and slowly improved our ratings as more users started liking us.