I all wondering if you can help! I know if you jail break your iPad you can download the app YouTube to mp3 but I've still not decided asa to whether I'm jailbreaking mine, is it possible to get something similar to YouTube to mp3 with out performing the jailbreak?!
GoodReader recently added a bookmarklet (you add it to Safari) that will download HTML 5 videos to itself.
Tap the gear icon for Settings (in GoodReader), then choose General. You'll see a green 'bookmark for video' button. Tap it for instructions on how to add the bookmarklet to Safari; preferably to the Bookmark Bar.
In Safari visit YouTube's mobile site (because all video you see there will be HTML 5). When on the video's page, tap the bookmark and you will be taken to GoodReader where the video will be downloaded.
Here is a link to more bookmarklets you can add, and more complete instructions on how to add them.
I believe there are other apps that are specifically made to download YouTube videos. This is just the method I use for those rare occasions I want to do so.