One of the cool features in ASP.NET 2.0 and above is the app_offline,htm file. If you put an HTML file named app_offline.htm in your root directory, then ASP.NET runtime will re-start the application and redirect all requests to your web application to the app_offline.html file.
This feature is very useful when you want to update your web application do not want the users to see error messages which can come up as the files are being uploaded on the remote server. Once the upload/update process is compeleted, you can simply delete the app_offline file and the ASP.NET runtime will start serving the requests normally! In our applications, we always keep an app_offline.html file for each of our projects having a nice HTML message which shows up when the application is undergoing an update.