It struck me that the Page_Load code on page 259 to hide/show the treeview/menu depending on which theme you were using was not an ideal way to apply themes as you would have to make a code change with each new theme.
If you create a skin for the treeview and one for the menu in each of the themes, you can set the "visible" to true/false there instead to get the same result while keeping theme code in the themes themselves. In Monochrome, for example:
<asp:Menu runat="server" SkinID="navMenu" Visible="true"></asp:Menu>
<asp:TreeView runat="server" SkinID="navTree" Visible="false"></asp:TreeView>
(you would want to add the SkinID to the respective controls as well for this to work)
Would this not be the preferred way to do this?