Focusing on tech and scalability before getting users will just result in a well-engineered ghost-town. People would rather use something slow and buggy if that

Focusing on tech and scalability before getting users will just result in a well-engineered ghost-town. People would rather use something slow and buggy if that's where the activity is. It's much more of a marketing and PR challenge than a tech challenge. Having a site that works well would be nice too, sure, but finding a way to get tons of users signed up (and keeping them engaged) is far more important.