I did some research, and turns out that these exercises are more hype than help. Simply put, since sagging skin occurs mostly due to the loss of collagen, these exercises certainly won't create more collagen. And they can't undo sun damage that causes wrinkles either.
In fact, facial expressions are one of the major causes of lines and wrinkles in the first place. And while I'm not advocating that we all stop smiling and adopt netural facial expressions in the interest of preventing wrinkles, there is no need to encourage those wrinkles by using more facial expressions.
Think I'll skip the facial exercise DVD's and invest in a yoga routine instead.