The Canon EOS 40D isn’t technically supposed to be able to record video.. and in essence, it can’t – but some clever Russian guy has encapsulated Canon’s Live view trickery (you can see the results of Live view via your laptop with Canon provided software, so obviously it was possible all along, but he’s put it to more practical use).
I’ve posted a video up on YouTube at http://ie.youtube.com/watch?v=19Q08En4obQ and you can see the results of adjusting the focus manually with an EOS 40D and Canon 50mm f1.8 Mk II lens.
Obviously if you had a long USB cable, which can be obtained very cheaply these days and a small laptop in your rucksack, you can do a RAW recording from start to finish and roam around the place recording as you please at fairly high resolution, achieving some very interesting focal effects (with the right lenses of course!).