If you want to download youtube videos, this tips is what you want.
All you need to do is replace the youtube URL http://www.youtube.com by http://www.voobys.com
For example to download this video:
http://www.youtube.com/watch?v=nuzRsXKm_NQ
You need to enter this URL
http://www.voobys.com/watch?v=nuzRsXKm_NQ
Give access the plugin and just click on video resolution you want to download.
Very easy to do!