ScottGu posts an interesting work around for the App_Offline.htm feature of ASP.NET 2.0. This feature allows you to put a filenamed App_Offline.htm in your root directory and ASP.NET once it sees it, it will shut-down the application (app domain, requests, etc.) and redirect all dynamic traffic to it. So your end users will see the friendly message you've placed inside App_Offline.htm.
Well, it appears that the "Show friendly Http Errors" feature in IE6 prevents this from working correctly when the size of your App_Offline.htm file is less than 512 bytes. Work around? Well, make your file larger than 512 bytes. Yeah, I know it's cheesy but it gets things working.