How to download youtube videos in Safari?
There are a few extensions that will add a nice download button to the Youtube video page, and give you the option to download in various resolutions.


Youtube Video Downloader
Fastesttube
YouTubeDownloader


You can also try ClickToPlugin, which does a lot more than just offer a download link, but it does that, and it's one of my favourite extensions. Makes watching web video much nicer.