From next month the YouTube mobile app will let users download videos and keep them for 48 hours of disconnected viewing before they disappear into the DRM'd ether.
Users uploading videos can opt out, but in-stream adverts will also be cached and viewing figures will be uploaded once the device reconnects, so there seems little reason to take one's videos out of the system unless the copy protection proves massively insecure.
YouTube hasn't, historically, bothered much about protecting content. The business was built on copyright theft and while it's cleaned up a bit under Google's ownership the content has shifted to corporate-sponsored promotions and videos of cats, while Google would like to see YouTube competing with NetFlix and Blinkbox for viewer share.
The platform is already rented out to content aggregators like the UK's Channel 4, which uses YouTube to run its 4OD web service, but Channel 4 has to provide its own mobile client as the (Adobe-provided) DRM available in the website isn't utilised in YouTube's mobile version.
Offline viewing could make YouTube content more attractive, if Google can secure it to the satisfaction of the content owners. Either way, we'll have to wait until November to find out. If not, then it just means we can all legally download videos of cats dancing to watch next time we're on a long-haul flight.