You can directly insert web video into your PowerPoint presentations just the way you embed video in web pages. The video could be on YouTube, Flickr, MySpace, Facebook or any of the other video sharing sites.
Watching FLV videos in the browser is half the fun - you can do so many other things like split FLV videos into multiple clips, trim the introductory music, convert flv videos to MP3 songs, extract image frames from the video, etc.
This YouTube Video Tools directory has links to the best online tools to get the most out of YouTube videos. You can watch video deleted from YouTube, add sub-titles to videos, track statistics on YouTube and so much more.