Update: Check out the latest post on this subject here:
old_UPDATED: As of DECEMBER 2013 This method of downloading will no longer work due to Youtube’s modification of how videos are streamed. I have created and updated thread HERE with the most up to date method of downloading. The rest of this post will remain for those who are investigating multiple techniques. Thanks ProjectileObjects
Ripping Videos from Youtube for VJing Batch downloading and converting on your MAC
Click here to view the rest of the post!