Visual Studio 2005 comes with a handy configuration tool for your website.  You click on the little icon, and a website will pop up that will allow you to visually make modifications to your web.config file.

The problem is that each and every time you open this tool it adds the xmlns attribute to your configuration tag like so:

<configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0">

This effectively kills your intellesense (autocomplete) within the web.config.  Drives me crazy.  The obvious fix is to just remove that attribute each time, but what a pain in the ass.  Here's a better work around.

Go to C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\ASP.NETWebAdminFiles\App_Code and edit the WebAdminPage.cs file.

on line 93 in the SaveConfig method you find the line (unless you've modified this before):

config.NamespaceDeclared = true;

Set the value to false.  And you're done.