I think am not a big Nadal fan by any means, but I think his doubters will be in for a rude awakening in 2006 and beyond. This kid is the real deal, he still may be overrated by some people who say he can even win Wimbledon right now(he cant, probably not atleast for another couple years, or atleast until adapting certain parts of his game while playing on grass), however he has the talent, intensity, hunger, work ethic, and skills to stay at the very top, continue to be the guy to beat at the French, continue to challenge for Masters titles on hard courts, and contend for slam titles on hard courts as well. Players like Roddick and Hewitt will have a time time ever getting over him again, they already seem to have maxed out their abilities in alot of ways, Hewitt especialy, while Nadal still can grow and develop. The player who might benefit from having more opportunity to play him to figure out his game is Federer, Hewitt has won all his meetings with Nadal so understands his game quite well, it is Nadal who is getting closer to figuring out how to beat Hewitt based on their Australian Open match IMO, Roddick and Nadal have not played since 2004 and their two matches were a green Nadal on hard courts in the U.S, and Nadal vs Roddick in Spain on clay, both rather obscure situations to what a meeting between them now would be, so it is not as if Roddick has been able to learn much up to now how to play him.
I think he will learn from the scare near the end of the year of getting injured, and the brief fear it might force him to miss a longer period of time.
He will learn to be careful with scheduling, and how to take the right precautions in physical training and preparations, to mantain his great intensity and work ethic, without overworking and causing injuries.
The players most likely to give Nadal the hardest time in the near future are Federer, and Berdych who is the most likely of the other up and comers to crack the upper echelon soon IMHO. Roddick, Hewitt, Safin, Gasquet, Monfils, Nalbandian, Ljubicic, all have a huge challenge, not impossable for some of them, but huge nonetheless, ahead of them to keep up with Nadal.