There is a drawback to this, obviously. If your codebase is some scattered mish mash of Python, PHP, Actionscript, Javascript, Java, etc, your ability to reuse code diminishes at the language boundaries. You end up having to write very similar code to deal with the same objects on the client side and the server side in multiple languages, producing more code to maintain overall.<p>Unfortunately because of the nature of the web I haven't seen any real good solution to this yet. At minimum, you're usually dealing with some combination of Python/Ruby/PHP backend and some amount of Javascript/Actionscript on the frontend.