I'm working through NerdDinner and I'm a bit confused about the following section...

First they've added a form for creating a new dinner, with a bunch of textboxes delcared like:

<%= Html.TextArea("Description") %>

They then show two ways of binding form input to the model:

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Create() {
    Dinner dinner = new Dinner();
    UpdateModel(dinner);
    ...
}

or:

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Create(Dinner dinner) { ... }

Ok, great, that all looks really easy so far.

Then a bit later on they say:

It is important to always be paranoid about security when accepting any user input, and this is also true when binding objects to form input. You should be careful to always HTML encode any user-entered values to avoid HTML and JavaScript injection attacks

Huh? MVC is managing the data binding for us. Where/how are you supposed to do the HTML encoding?