Before or after, umbraco provide hooks. For all objects.
Umbraco 4 introduces a complete event model developers can use with their own applications. Everything in umbraco 4 is covered by this model, so it is possible to subscribe to any type of event, anywhere in umbraco.
Developers can, with very few lines of code, detect any event in umbraco, and execute their code accordingly. This makes it extremely easy to integrate 3rd party systems, such as back-up and workflow engines.