@pg I think a great one would be "b2b customer acquisition". This was one of those things that we realized was CRAZY HARD and (anecdotally) I've heard a few other YC startups who have run into this wall. Stuff like inside vs. outside sales, lead generation techniques, hiring salesfolks, adwords, etc.<p>Of course this stuff only applies to maybe 25% of YC companies out of the gates (tho eventually, even the consumer plays have to hire ad-sales guys).