Answer:
77% of students in the class of 2011 were in the top 10% of their high school classes. The average GPA was around a 4.4 and the SAT average was just over 1300. Though they may cut you a little slack if you come from a really tough high school such as one of the big Charlotte schools, these are good ballpark numbers to shoot for.
I am graduating from UNC this May and I know many people that fit the profile above, but I also many who don't. If you are remotely close to the profile and have time left start getting involved with your school and community. In addition try to work on getting letters of recommendations early - try your principal then work your way down to your teachers. Most schools ask for three try to get four or five, more cant hurt.