I tried to recreate the sample from ScottGu's first MVC post (http://weblogs.asp.net/scottgu/archive/2007/11/13/asp-net-mvc-framework-part-1.aspx).

When I define the Categories.aspx view as mentioned in the article, Html.ActionLink method generates the hyperlink /Products/List (omitting the category):
<li><%= Html.ActionLink(category.CategoryName, new { action="List", category = category.CategoryName})%></li>

But when I change this to the following, it works and the category name is added to the hyperlink:
<li><%= Html.ActionLink(category.CategoryName, new { action="List", id = category.CategoryName})%></li>

I didn't change the routing in the global.asax.cs. Can someone explain why the first code is not working as expected? 

With kind regards,
Taco Ditiecher. 

I found my mistake; I tried adding a new route to the routing table (in my global.asax.cs), but I placed it after the existing ones, instead of before.

The following code did the trick: 

protected void Application_Start(object sender, EventArgs e) {
	RouteTable.Routes.Add(new Route {
		Url = "Products/List/[category]",
		Defaults = new { controller = "Products", action = "List", category = (string)null },
		RouteHandler = typeof(MvcRouteHandler)
	});
	RouteTable.Routes.Add(new Route {
		Url = "[controller]/[action]/[id]",
		Defaults = new { action = "Index", id = (string)null },
		RouteHandler = typeof(MvcRouteHandler)
	});
	RouteTable.Routes.Add(new Route {
		Url = "Default.aspx",
		Defaults = new { controller = "Home", action = "Index", id = (string)null },
		RouteHandler = typeof(MvcRouteHandler)
	});
}