I don't want to sound "preachy" but just as a side note, the fact that a
music is in youtube does not mean it's "free". Actually, sometimes youtube is
forced to delete some videos because they have a non authorized soundtrack
and someone noticed it.
If possible, for your own protection, just listen to the music while playing
it in youtube, that way you are not really "keeping the file".
As for the site you mention, you identify yourself through your IP address,
so that could be a problem if laws like PIPA, SOPA, and others even worse,
came to pass.
As a suggestion, try spending some time on these websites, you might acutally
find musics that you like, and artists that you identify yourself with.
www.libre.fm
www.freemusicarchive.org
www.jamendo.com
All these websites are TRULY respectful of copyrights and musicians as the
creators of the music. You can have great songs, high quality audio, free
licenses, and you can download them directly which is better than converting
youtube.
Also, you can promote and support the artist himself, since he is the one
giving you his content.
Hope it helped you in some way.
If you want, you can also have lots of free movies, without worrying about
copyrights. Have a look around the forum, and if you can't find the comments
where we discussed it, feel free to message me and I will give you links to
free movies (as TRULY free, not "free illegal download) that suit your
tastes.