Well, they definitely don't solve the problem for the user, as the grey boxes inevitably aren't the same shape as the content that eventually appears, and the jumping around is still there. Text fields are often variable length and can reflow. Buttons are also frequently dynamic, and all sorts of widgets may not just line up. Sometimes, incomprehensive design changes cause further disalignment between the skeleton and the actual content.

It's sad and funny that the YouTube app seems to have just recently jumped on this bandwagon (either that, or the situation worsened so much that I started noticing how bad it is).