This trick has been mentioned on blogs before but it is such a useful and little documented feature I though it was worth a note.
If you place a file name App_Offline.htm in the root of your asp.net 2 application then all requests will result in this page being displayed.
Perfect for doing maintenence and keeping your users informed, just remember that the page will be delivered from the requested page location (e.g. it could come from a subfolder not the root) so make sure any references to resources, like images or stylesheets use absolute or root relative paths.
HTH
Ian
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