A couple months ago YouTube was down for an hour or two, that's the only time I've first hand experienced it. Sometimes you'd get the page to load, but not the video, sometimes you'd just get some Google error page.

The tin foil hat in me always assumes the worse, that it's a result of some unfriendly actors because that seems more likely than a company the size of Google having single points of failure and the ability for widespread outages like this as modern as they are.