Open YouTube URL to video. Append URL with &fmt=22 to view HD video
Show up Activity Monitor (Command-Option-A)
Seek for file with largest size and Option-Click it
The download should be started with default name video.mp4
rename the file to what you want
Using a program called get tube
you can download it here
Using mozilla firefox(the latest version)
Bookmarklet to Download YouTube HD
Here is the bookmarklet:Youtube hd dl
You can find this one on this url
Drag it to your Bookmarks Bar
find a YouTube video thats available in 720p
Click on the bookmarklet and a window will be shown to you.select save file and it is done.
a great free add-on for firefox called fast video download 2.03
click add to firefox and just wait 3 seconds.it will be installed .then select a 720p video and click one paused download located down on your browser.it is very easy.
two useful sites
with this one you can download and save youtube and other vids to your mac as flv or mp4 files-extensions.
you can choose any youtube vid and edit video and audio formats and many other preferences for your video you like before saving it to your mac.
i hope this wil help a little guys ...i think these are the 4 best ways to save youtube vids .