I'm using YouTube Downloader with success.
If you're using FireFox, add the Download Helper add-on, then you'll be able to easily download YouTube and other flash-based videos (and other media as well).
Then, to convert it to an iPad compatible format, use MPEG Streamclip (free, converts from/to many media types including transport streams, runs on Macs or PCs)…
Squared 5 - MPEG Streamclip video converter for Mac OS X
I tried many programs that convert Youtube video and save it to my Mac. Most of all I came
MovieSherlock. This software converts video to audio, is looking for any video with no problems, keeps
the music automatically to iTunes and I can send it on the iPhone. Takes very little time and very
convenient. I advise it.
If your iPad is jailbroken, then it's easy to save.
There are many ways like
1. Use "Mxtube" (Free)
Just download it and search for the video and there will be the option to download.
2. Use " ProTube" (Paid)
Better than Mxtube. You can sign in to your own Youtube account. Pixels is allowed to choose. You can download to MP3 too.