when I was in college, I became aware of the verse about what we allow in our mind actually mattering (Romans 12:2). now i listened a great to rock back then. long drives drives from Fort Collins to Creede made for many hours of music listening - and I thought about this verse.....
so i contrived a test: i set aside six months with no rock music (at all!) and only listened to Christian talk radio.
first, i have to admit addiction withdrawals from rock right off the bat! and utter boredom with Christian radio. but with some work, I was able to find shows which were solid teaching and concentrated on those for my listening or recording and playing back later on my drives. (like Thru The Bible, Charles Stanley, Adrian Rodgers, etc)
by the end of the six months, I noticed some interesting changes: i was now very critical of the words to songs I enjoyed, i knew a great deal more about the Bible and Christian life, and I suddenly found I was knowing answers to people's questions. unbelievably, i also found that i would drive slower so that i would not arrive home too soon. go figure.
yes, i too enjoy the mayhem on youtube but find myself put off by the swearing and risque or outright rude nature of some of it.
if you consider this life to be your learning and trial ground for the rest of your life - in Heaven or in His service, then yeah, what you are allowing in your mind does matter from both an Earthly and Heavenly sense.
Meditate on Romans 12:2 and wonder where God could be leading you if your mind was to be His.....