A software [JDownloader][1] will really help, if you copy a youtube link to clip board it will give you various options like
download .mp3
download .flv
download .mp4
download in 320, 460, 720 etc

moreover if you copy a Youtube playlist link, it will parse all videos and gives you option to download all the videos in playlist

Supports plugins for more than 200 other sites like (hotfile, mediafire, ifile etc etc)

Must give it a try, it will be your universal downloader

one more thing, it supports multithreaded downloading


  [1]: http://jdownloader.org/