Usability 
YouTube's mobile site offers the full catalog of videos from the desktop YouTube site. An update adds social sharing features and direct video uploading.
You need to login to access to the new capabilities which include the ability to post comments on videos, share videos with other YouTube users or by Email, add videos to my favorites or to a playlist and rate videos. At one time the YouTube mobile webapp supported uploading videos directly from the phone but that feature was removed. You can upload phone videos to YouTube using MMS or Email to your personal YouTube email upload address that can be found on your YouTube account profile page.
I'm impressed with YouTube's approach to mobile. It is one of the very few video sites I've seen that has thematically consistent URLs across all devices and browsers. That means that any YouTube video URL is device independent and will work in any mobile or desktop browser. I can click on a link to a video on a mobile or desktop site or in an RSS reader on my phone or on the desktop and the video will be delivered in a format appropriate for what even device or browser I'm using. It just works and means I can safely share YouTube links without having to worry about the context (Android, iPhone, Opera Mini, feature phone browser or desktop) that they will be viewed in.
