If you've been reading AP in the last 24 hours, you probably saw our hands-on post with YouTube's new Share tab - it's actually very neat. But if you wanted to see and hear the new share tab and chat features explained, just check out our YouTube video, in which we explain YouTube, on YouTube, for you. I'll let Mark take it away.
Edit: Unfortunately, the invite links expire so quickly that sharing them would just be impractical - we'd have to update this post every 20-30 minutes. If you've been invited to share, share your own invite link in the comments to keep the invite train going!