Nested Master Pages
As I was working up my talk on Visual Studio 2008 and started working on my Nested Master Pages. Oh my gosh, it actually works.
I created this parent master page

I then created this child master page
And then the result was this page

You might not be able to see it, but I can edit the child page just like I thought I could. While I don't use Master Pages in any major way, I definitely think this is a really cool WOW feature.
To put this into a simple display of information, here are the simple versions of the various files.
MasterPage Parent file:
<%@ Master Language="C#" AutoEventWireup="true" CodeFile="MasterPageParentSimple.master.cs" Inherits="MasterPageParentSimple" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Untitled Page</title>
<asp:ContentPlaceHolder id="head" runat="server">
</asp:ContentPlaceHolder>
</head>
<body>
<form id="form1" runat="server">
<div>
Simple Parent Master Page.<br />
<asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server">
</asp:ContentPlaceHolder>
</div>
</form>
</body>
</html>
MasterPage Child file:
<%@ Master Language="C#" MasterPageFile="~/MasterPageParentSimple.master" AutoEventWireup="false" CodeFile="MasterPageChildSimple.master.cs" Inherits="MasterPageChildSimple" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
Simple Child Master Page<br />
<asp:ContentPlaceHolder ID="Content3" runat="server">
</asp:ContentPlaceHolder>
</asp:Content>
ASPX file:
<%@ Page Language="C#" MasterPageFile="~/MasterPageChildSimple.master" AutoEventWireup="true" CodeFile="DefaultSimpleMasterPageExample.aspx.cs" Inherits="DefaultSimpleMasterPageExample" Title="Untitled Page" %>
<asp:Content ID="Content1" ContentPlaceHolderID="Content3" Runat="Server">
this is some basic content.
</asp:Content>
IDE View:
Resulting output:

Javascript Intellisense
While it doesn't seem to solve every problem, calling "devenv /resetsettings" does seem to resolve some of the issues that I am having with Javascript Intellisense. It might be worth giving it a try to see if it resolves your problems.