It can be very entertaining, although very time consuming. Youtube does a decent job of blocking out adult content, but there is still some suggestive content on here.
YouTube is a wonderful site when you are bored and want some humor, or to watch a tutorial about something.
It's the best video hosting site. There are many interesting videos, and a few which are not. In overall, it's a very good and safe site. BUT: be careful when clicking on SHORTENED links in video descriptions, they aren't always safe! (Especially when you're looking for software cracks or similiar)
I like it for it's free speech venue. But would not want my child surfing around learning how to commit criminal activities. Ie... lock bumping, lock picking, and any number of other skills that a child doesn't need.