Nifty hint that could be extended to do fancier stuff. I must say that I think the new Dropbox iPhone client is brilliant. Being able to view and/or email a link to a document to someone while on the move will probably save my vegetarian bacon one of these days.

"So here’s what you do: create a “Pre-Dispatcher” that intercepts the CGI requests before the Rails dispatcher gets to do its job. If everything’s OK, pass the request on and all is well. But if there’s a problem, then render a pre-defined controller and view."