Heroku node maintainer here. No official docs yet (it's like an hour old already! :) but it works about the way you might guess: use engines.iojs instead of engines.node in your package.json.

(screencast: https://twitter.com/HunterLoftis/status/555234067520565249)

We're also excited to see node hit a 1.0 and merge in new V8, ES6 features, etc. I'm especially excited about Cluster's round-robin load balancing which has been a compelling reason to use 'unstable 0.11' for a while.

Heroku has pretty good node support, but I'd doubt they support replacing the binary yet, so you'd have to wait for Heroku to support that.

For manual deployment, the single iojs binary and your project folder should suffice, along with a way to start/restart your app automatically.