There is a ton of good content on YouTube, but copyright infringement claims and DMCA take-down notices mean that any given video can disappear at any time. Having a local copy of the video means you won’t lose access if YouTube removes the video from their site. And if you convert the video to MP4 format, you can transfer it to your iPod as well.
There are two excellent free services that take YouTube videos, download them to your hard drive, convert them to MP4 format and add them to iTunes. For Windows users, try iTube, available here. Mac users should use PodTube, although it requires the use of Safari.
If you just want to get access to the file and view it directly (the VLC media player will play flash-format video files) and/or convert it to another file format, you can download any YouTube video using Oyoom, or try the Firefox extension called Video Downloader. We’ve also written our own tool to download YouTube videos, available on this page, and it’s also embedded below. Just enter any YouTube video URL and hit the “Get Video” button.
http://www.techcrunch.com/wp-content/themes/techcrunchmu/youtube_download.phpFor true do-it-yourself’ers, Erica Sadun at O’Reilly has the step-by-step here.
Once you have the .flv video on your hard drive, view it with VLC, or convert it to another format. For Windows users, try Replay Converter. For Mac users we recommend iSquint. There are also a few online file conversion services, but they are not as reliable as desktop software and you have to wait for both the upload and the download.
For additional YouTube tools, see this site.