We launched our site with only one machine (dedicated host I think we paid about $100/mo for it as well) and had stories about us on the big blogs (TechCrunch, Gigaom, etc) - it performed like a champ. I guess it depends on what your app is like though.
Awesome, good to know.. I was a little nervous that I didn't have a massive cluster ready to go ;) I'm just going to make sure my database indices are in the correct places and see how launch does.
