We've added a lot of new tools and functionality to the YouTube APIs in the past year (we launched the new Google Data-based API last August!), and we recently gave our overview page a face-lift to help developers figure out what will work best for them.
The new Getting Started Guide goes more in-depth about each of the different offerings. For example, we want to highlight the efforts of the AJAX API Team in providing the Video Bar and Video Search Control widgets that can be easily embedded in any website. These tools allow you to surface YouTube content on your site with minimal effort. There are also summaries about our player API offerings and the in-depth integrations possible with the Data API.
If you've been meaning to add a little (or a lot) of videos to your applications, now's a good time to check it out :)