JSF is stateful, so you need to have sessions replication if you're going to have clustering. So all of your session beans get replicated, if a node dies, another will be able to serve the request. Don't expect to scale much with stateful designs.
If you want to avoid this, you can put a hash of user identity in cookie and check on each request, so you move to stateless. JSF 2.2 will have a stateless mode.Stateless is the way to go but it's hard to acheive.