The first two dogs my wife and I had were mutts, 1st was a half black lab half dalmation (all black though) that was one of the best dogs I've ever had, second was a black lab mix that was the most problematic dog I've owned. After our mixed experiences we decided to research our next dog heavily and stick with a purebred.
We decided on a Newfoundland after a lot of research in different places, and it was a great decision for us. We had Thor for five years, but his life was cut short when he got out of our fenced in back yard and was hit on the road in front of our house. Our newfie was great with our young kids (both infants/toddlers at the time) and was the best dog we've had. We wanted another Newfoundland, but it was too painful to get another right away, so after some more research we decided on a Saint Bernard. Our Saint is very close in temperament and manners to our newfie, and was our first female dog. I watched both the Saint and Newf videos linked in the original post, and wholeheartedly agree with what was said.
I've had numerous friends get dogs without doing much or any research, and in most cases the relationship was short and unpleasant.