Download Firefox, then install the add-on "DownloadHelper". This allows you to download flash videos. Then convert the flash movies with FormatFactory. That's how I do it. Good luck.
1. jailbreak your iPhone or iPad using Spirit 2. go to cydia & install MXTube 3. use MXTube to search youtube videos & download inside 4. you can either use iFile or MXTube to view these videos