A new and updated version of Youtube's mobile layout can be enabled at m.youtube.com/new_visual_design from your iPhone devices (on both iOS 4 and iOS 5 beta). The layout is opt-in and needs to be manually activated through the above web-link. However, trying it on Android 2.3 or BlackBerry 7 OS devices yielded no new results as of now.
Macstories.net - Once enabled, the new design brings a much darker color palette that presents videos against dark toolbars and buttons — I assume this should make videos a little easier on the eye, but the effect is sort of ruined by Safari’s blue address bar. Unlike the standard mobile layout, launched last year, when saving this new design to the iPhone’s Home screen you won’t get a Retina-ready icon or full-screen web app. This, again, should be related to the experimental nature of the design.
The new mobile layout brings updated buttons and a new toolbar to toggle HQ on videos, give them a thumbs up/down, and share them. The HQ toggle comes with a neat fading animation and the video thumbnail has new loading and Play controls, too.
Check out this link for more screenshots.