(Written 12/27/10)
Frustrated with the way YouTube is constantly changing their site so you can’t download their videos? I was for a while. But there is still one way that I know of that will still work. And it works quite well. 
The only requirement is that you are running a recent version of Safari. Download the linked Safari extension, install it, and then click on the “Download” button which should now be placed above YouTube videos. You should then be able to select a format and size (I prefer MP4) to download.
Download extension from external site
Advertisement
