If you look at players who Nadal has most difficulties with beating, than it seems quite clear the hitting flat and hard is really the best way to "try" to beat Nadal. Of course on clay it's not going to be easy, but Matthieu got Nadal nearly to a fifth set last year at Roland Garros. Davydenko pushed him till three sets last week. And I do actually believe, that if Safin has a "on"-day, that he could actually be a danger to Nadal. That is if he doesn't loose in the previous rounds at Hamburg. He would probably have some troubles with a young Agassi on clay as well.