Ditto. I handled hitting the front page of /., digg, and yahoo tech on the same day on a single dual core server. The site slowed down a little during the worst of it, but page load times were always reasonable. Unless your app is a total beast and/or you require a large amount of resources to service each user, a single server is probably fine.

when we launched younoodle we hit NYT / techcrunch / venturebeat within a few hours. me and the other engineer slept through it and the site didn't go down once - it even stayed pretty fast throughout that day. btw, techcrunch doesn't send much traffic at all, we got more from delicious.