"Isomorphic JavaScript" is gaining traction—write code that runs on both server and client. Render on the server for fast initial load, hydrate on the client for interactivity. The promise is having your cake and eating it too: server-side performance with client-side dynamism.
After building a few isomorphic applications, my take: it's powerful but not simple. You're not writing code once, you're writing code that accommodates two environments.