I actually agree that Hughes is overrated, I think he's a very good player at a young age, however there are a few too many holes in his technique for him to be consistent in all conditions right now. There's no questioning his success so far however we're yet to see him face quality spin and to see how he copes with slower surfaces where the ball doesn't come on to the bat. Also it has to be mentioned that the South Africans bowled absolute tripe for 3 out of the first 4 innings of this series.
His rather devil-may-care temperament won't help either but one can expect him to settle down after a while. I think the most interesting phase in his career may come a bit later on, when Ponting decides to finally hang up his boots, there'll be a few others going around that time too, Hussey, Katich, Lee, Johnson will be over 30, Clark will probably be gone, there aren't too many ready replacements knocking around Aussie cricket. Batting at the top of what may well be a fairly weak Aussie side (He and Clarke will be the mainstays) will put a huge amount of pressure on him to keep his wicket, it will be interesting to see if he can keep it going.