Once I started playing around with this and watched some of the videos, I lost track of time. I have used youtube before but mainly to view movie clips, video clips etc, not for educational activities.
My son needed to tie his tie correctly and guess what, they have a video for that. So yes some of the instructional videos can certainly be useful.
Youtube etc is blocked at our school so I had to access this from home. I did find some clips stop and start so for educational purposes this could be a bit of a pain.
Having said that I had a great time watching clips. I loved Conan the Librarian