From John Galloway [asp.net] Popup Tester Web Control
This is a great idea - an ASP.NET server control that only shows if popups are blocked. Use it to show a warning message, info on how to disable popup blocking for your site, or the information you would have shown in the popup if it was allowed.
Now that all the browsers are including popup blockers, this kind of thing should be required in pages that still use popups.