I found this article about our throw-in completion rate and goal rate stemming from throw-ins to be quite interesting. It is of course hypothetical but it raises a few eyebrows: http://www.mlssoccer.com/news/article/2012/08/07/central-winger-houston-have-weapon-throw Note that I don't actually think throw-ins are the secret to our success. That, of course, comes from the spirit of Waibel.
When I was playing youth soccer, long throw-ins weren't a taught skill. There were just always some kids with long arms that could throw the ball freakishly far for some reason. I've got long arms, but I suck at throw-ins. It was always just a mystery.
I don't know why. My HS team scored a ton of goals off of throw ins. Myself and another guy on the team could put the ball in the middle of the box from the sideline. For our team, it's all about keeping that prized possession. Dom would beat these guys with a stick if they started handing the ball over on these gimmes like other teams do. Doing the small things right!
I wish they would have taken it a step further and show how many goals actually are scored off the long throw. My inclination . . . not many. While dangerous, it always seemed like more of a 50/50 ball at the pro level as it does not have the pace of a free kick thus getting to the target slow enough for a defensive reaction. Of course, I can think of one that worked.