via Fritz Onion: (bolding mine)

I went to one other presentation by Scott Guthrie at VSLive! this week where he presented 'tips and tricks' for ASP.NET 2.0. If you're interested he has posted the slides and samples on his website http://www.scottgu.com (it's currently the first entry on the page) - highly recommended.
Anyway, the one feature he presented that I hadn't seen before was the VirtualPathProvider in 2.0. This class essentially lets you decide where file content comes from when a request comes in, eliminating the need for any physical files on the system.