Quoted: In June 2005, YouTube revamped, adding the four essential features that jump-started viral growth. 1) related video recommendations, 2) one-click emailing to spam a friend about a video, 3) more social networking and user interaction tools like video comments, and 4) an external video player.

Quoted: This tells me that there is plenty of room for more services to provide these types of services, despite the exhaustion some of us feel every time a new one emerges. It also indicates that there is something far more interesting about Digg than the size of its contributing users.

Quoted: So why such massive growth? One theory is that YouTube tapped into MySpace from early on with their video widgets. With social sites, getting a few thousand key users from the start can lead to a huge snowball - it seems that the network effects kicked in early here. There’s also the fact that YouTube made the process super-easy, and chose to use Flash from the start - this ensured compatibility with most browsers.

Quoted: The social features are impressive too: YouTube realized that the creative class wants to interact with media, so they were sure to add commenting, groups, favorites, user ratings and all kinds of social filters to help you find the best stuff. What’s more, they continually add new features: if you’ve used the site in the last few days, you’ll have seen that YouTube now prompts you to view related videos once the current one has finished - you can even hover over the video to skip to the next clip. Clearly, this is a trick to make sure users stick around as long as possible.