its the same as it have always been.
We keep the deployed archives in sync and JBoss picks up the changes it can see dynamically - those changes are mostly html and xhtml.
Class changes such as a servlet was never automatically picked up unless you touched the descriptor or restarted the module.
We never automatically triggered a restart of a module because until AS7 it would be a rather long wait in most places.
We are considering adding a "restart module on when <path expression, defaulted to "**/*.class"> changes"