The more I work with Ben Tiedt's excellent Community Server Chameleon architecture for controlling page display the more I groove on it. I can't believe the guy uses a MacBook...
Anyway, here's a nuglet describing how I extended the Community Server Master.master file on a client site over the weekend to control its output based on the application.
Let's say you have a footer that you only want to show on all site areas except the forums area. Rather than creating a new common/.Master page for forums, extend it using Chameleon Intelligence.
<asp:ContentPlaceHolder ID="footerContent" runat="server">
<CSControl:Placeholder runat="server" Tag="Div">
<DisplayConditions Operator="NOT">
<CSControl:ApplicationPropertyValueComparison
ApplicationType="forum" Operator="EqualTo" runat="server" />
</DisplayConditions>
<ContentTemplate>
This displays the content on all Community Server areas except Forums. Neato.