If you've ever embedded a YouTube video into a Web site or a blog, it's now just as easy to add one to a PowerPoint slide using PowerPoint 2010. Just go to the Insert tab, click the button half of the Video button, and select Video from Web Site:
Now just cut and paste the embed code that you get from YouTube (or any other embeddable Web video player) and then click Insert:
But there's an even easier way: Get the third-party YouTube Video Wizard (not supported by Microsoft). This add-in allows you to simply enter the YouTube video link - though you'll still need to use the embed code if you want to add videos from other sites.