He goes on to explain why: We were based on some fairly heavy technologies (natural language understanding, conversational dialog, context, local search, plan-based service delegation, PCI-compliant data stores, machine learning), and it took us two years to go from our initial prototype to something ready to deploy and scale. A few weeks after we launched, Steve Jobs called the office and the rest is history. As a startup, we were potentially competing with large companies with lots of resources (e.g. Google, Microsoft), and we needed a good running head start before anyone knew precisely what we were trying to accomplish.
For a more user-facing, social website where getting the right features is important, don't be stealthy, just get it up and iterate (c.f. http://change.org). But if you have a technology that takes some time to get right, being stealthy enables you to have buzz when you emerge and the head-start you need to compete with anyone.
Here's the link: http://www.quora.com/Stealth-Startups/Is-there-a-single-exam...