OK, I might be a little late to the party, but I just read about ASP.NET support for easily displaying a holding page while updating a site. Previously I’ve deployed a 2nd website with the same host binding, then stopped one and started the other. I’m now a little embarrassed…
If you create a file named App_Offline.htm in the root of the web application, asp.net will shut down the app domain for the application and return the contents of the file in response to all requests. Once you’re done updating, delete the file and normal service will resume. Much simpler, especially if you’re deploying via FTP.