Part of the controller? I have heard people claim that ActionForms were part of the model, but I don't see how they could fit into the Controller category. I consider them part of the View, but I see that they can bridge between layers.
I actually put a lot more code in my Forms that I think most people do. I treat them as a "View Helper" where I can throw methods that will reduce the amount of scriptlets that I need in the JSP. I also have "setData" and "getData" method in the form that handle the translation between the data objects returned by Toplink and the form fields. The form does not seem like a great place for this code, but it enables me to get a lot of reuse at the Action layer (the generic save action just needs to call the getData method on the form and pass the object returned along to the business tier).