I guess I'm in the minority because I love the blow out I love the volume it gives her. It gives her an air of authority that matches her position. Finally it is a glimpse of middle age Kate and I like it. There is nothing wrong with long hair as you get older I think the key is not looking like a kewpie doll with girly curly spaniel hair it should be more sophisticated. I still think she could stand to take another 3 inches off the bottom and not lose the vibe of long hair. You don't want her in Mathilde mode but getting away from cutesy poo would be nice too and don't get me started on Mary's stupid 70s wings.
I like the blowout too. She wore it in much the same way for Charlotte and George's first day of school this year. Long hair is fine as long as it doesn't thin out, if it does then you need a cut.
Had to laugh at the wings comment. I've grown my hair out, permed it (once was enough) and wore it in layers for years. Now the layers have all grown out and it's shoulder length again - just like high school without the wings. Back then you either had a Farrah Fawcett, Dorothy Hammill or wings.