Sports Illustrated had a piece on their site going into depth about the Nadal movement after he lost in Australia. The piece interviewed Patrick Morutaglou - who's been a Nadal fan for a long time. He's adamant about this subject: Nadal is much slower than he was, and Nadal himself is aware of it. Patrick said in the height of his prime, Nadal was still hitting short like he is today. The big difference is that back then, guys were much more reluctant to come in on the short ones. Nadal's foot speed and foot work we such that he was not only able to get to the ball but was able to do something with it - either get back to neutral or hit an outright winner from an impossible position yards behind the base line. That's what he cannot do anymore - cover that ground when he hits short. Guys are now stepping in and wailing on his short shots, and getting much better results than they were as recently as 3 years ago. Morutagolou was pretty blunt about his prospects: they aren't good. The fact that Nadal is seeking more spin by switching to Luxilon - just as he sought more spin when trying a new stick last spring - tells us what he thinks the solution is. But if he thinks that, it shows just how grim his situation is today. A slower moving Nadal is a Nadal who hasn't too much of a bright future left on the tour.
