Seeing if people are willing to pay for it is still a great metric. But until (if ever) the advertising bubble actually pops, extremely few web products will be

Seeing if people are willing to pay for it is still a great metric. But until (if ever) the advertising bubble actually pops, extremely few web products will be best served by freemium. I can count web freemiums that made more money than their free counterparts on half a hand.