Robin Good: If you are looking for an easy solution to your need to either download or convert YouTube videos, WonTube has a solution that works well while being fully integrated with your preferred browser.
Whether you like Chrome, Firefox, Safari or IE there is a dedicated "add-on" for you right on this page: http://www.shareyoutubemp3.com/addon.html
Once installed, go to any YouTube video and you will see two new green buttons right above the clip.
The first one, allows you to download any YouTube video at your preferred resolution, from HD 1080p to FLV low-quality at 240p. You choose.
The second one allows you to download the video clip as an .MP3 file.
Very useful. 9/10
An Android version of the video downloader is also available here: http://www.wontube.com/free-youtube-downloader.html as well as free desktop versions for PC and Mac video converter tool http://www.wontube.com/free-video-converter.html
More info: http://www.wontube.com/
Try it out now: http://www.shareyoutubemp3.com/addon.html
N.B.: No ads, no registration, no fee (no business model, and no names of people behind it. The add-on browser version seems to carry no threat whatsoever).