Back in YouTube's "golden years" (05'/06' ish), one could practically find (technically an understatement; "A:F6" anyone?) on YouTube, let alone porn! I will say on-topic that it was YouTube that introduced me to softcore model Michelle Lynn (mostly non-nude, with extremely rare teases if any). Today, you won't any of her vids on YouTube.
YouTube has changed a lot since then, stripping (for a lack of better words) down on what stays and what doesn't; so like other posters have said on this thread, it's mostly educational stuff that you get to see any more skin than many of the webam strippers will show you (and I tell you there were PAGES of them (filtering fail) before I could get to that one webcam vid of the guy who was dabbling with the functions of his and turned himself into an animated shark...remember that one?)
I never had a chance to see the vid I heard about where someone commented "I'm 12 and what is this?", but I'm not a hardcore lover anyway.
I also say: it depends on the fetish. If you're a GTS-phile, like I am, YouTube will remain a place to feel---"really excited" (why did the Jenna vids have to fade away, those were awesome!).
*hears folks coming*
I'm 24 and what is this???