There are a ton of ways to gather YouTube videos, but not all let you grab the new higher quality ones. On the AE-List, Brian Maffitt of Total Training offered a way to gather YouTube videos using Apple Safari (not the best browser), even the new higher quality ones:
"Use Safari [it works on Mac and Windows]. Open up the activity window in Safari, then load the YouTube page. You'll see the asset show up in the activity window, and it will be obvious because it's the only one that shows you streaming progress. Just double-click [or option double-click and rename the download] on the item in the activity window (you don't need to wait for it to finish streaming) and it should automatically download. You can do this with regular FLVs as well."
Update: On Windows, Control+click in the Safari Activity window downloads the file as HTML. If you then rename it to FLV or MP4, the file plays in Adobe Media Player, K-Multimedia Player, Real Player, FLV Player (as flv), and VLC -- but not QuickTime Player. Only VLC is incapable of scrubbing. When I tried the same process in OS X 10.5.1, I could download the file as HTML, couldn't play it.