Amazon managed to beat Apple to supply (legal) downloadable videos.
Really strong idea, but the DRM supposedly won't allow burning to DVDs. Silly rights holders shooting themselves in the foot again.
I don't think this will herald any significant change in people's buying behaviour. Personally I think big changes in buying behaviour will only happen when things are easy.
Although this is a nice system, it's nothing new. When you can hire a film from your living room (like with Homechoice) that's when you'll see a shift in behaviour.