Yes I find it really useful, and its the main component in DILD in a sense. Now, in ETWOLD, I find the exercises to be a bit overdone. If you can train yourself, and create your own way of building up your prospective memory it will grow onto you alot easier and also help with your lucid dreaming alot. Find your own way, whether it be simply reminding yourself to do a reality check or anything else. It doesn't have to be done the way the book explains in order to get it.