There is about 1 in 1000 chance of him not making the top 100.
Top Juniors who fail to get there are the ones who don't win men's matches at 16 or 17. Of course, there are one or two who don't make it even though they were good at the men's game at a young age - Yeu-Tzuoo Wang being a great example (although he did get to the top 100 for a while). But very rarely do people who were winning Challenger matches week in and out at 17 not crack the top 100. I would be shocked if you could find me a few examples from the last five years.
In case you think that Donald Young is overhyped, remember that he is ranked ahead of where people like Andy and Djokovic were at his age, and that with fifty times more the pressure to perform.
And as far as the Americans having a boring style is concerned... Well, beauty lies in the beholder's eyes and hence different people have different choices. You enjoy watching clay tennis which is made up of 100 stroke rallies ending with an unforced error. I quite like watching people like Roddick and Fish play.
And what rubbish is that? My dislike for Nadal isn't irrational at all!
1) He sneaks in his lackeys into tournaments across the world with the excuse of doubles. Feliciano Lopez at Queen's was harsh, but that was an innocuous little incident when you compare it to what he did in India this year. A wild card went to Bartolomeu Salva, his childhood friend, who was ranked outside the top 400 at that time.
2) Is probably the biggest Appearence Money 'criminal' out there after Gonzo and Roddick. He signs up for tons of events he never had plans to play, and poor souls (i.e. people who don't read SteveG!) who paid a lot so that they could see him in action end up seeing someone like Albert Montanes and go home.
3) What happened at this year's DC annoyed me more than all the other reasons! Nadal came up saying that he would miss the tie because he was injured (or rather, he had plans to get injured). Shouldn't an injured person take rest? Well, he returned for an exho that's played just two days later - http://stevegtennis.com/results/2007/ex-mallorca.txt I understand that top players can't afford to play Davis Cup all the time (I want Andy to stop it soon), but how about telling that to people instead of making excuses to fool crowds? I was stunned that he didn't get into trouble because of that.
There are probably loads of other reasons, but I'll stop here.