I'm more and more of the opinion that EC2 only makes sense for very small (2-3 node, no significant load) or very large (Netflix) deployments, and almost everyone else would be better off with either Linode-style VM rental or actual dedicated servers, depending on their needs.

The only exception I've seen are people with very spiky traffic patterns, who can save a bit of money by only running instances when they need them - but even then I suspect that the money saved might be less than you'd think.