Three things:

First off: work for yourself. (I'm 17)
I got a serious job over the summer working for a medium sized business, and the owner walked in and introduced herself as "the person who signs your paychecks"
Now I'm applying to business school

Secondly, one of the most valuable things I have learned is the importance of a paycheck. Whether it be an elder, a potential business partner or an idiot referee, a firm handshake while looking them straight in the eye makes all the difference in the world.

Finally, I've adopted the "F what people think" kind of attitude over the last year, I've broken down social barriers with my peers and feel like I have expanded my horizons so much because of it. There are now so many more people that I can actually "talk to" or add to my list of contacts. Most important to me though, is that I won't regret not doing something that I wanted to do thirty years down the road.

Take 'em or leave 'em, thats what I've learned amongst the rest of the academic hoohah in the attempt to prepare for college.

(BTW, I've never read Dale Carnegie, but my mother (pilot in the 1970's and 1980's) raves about him)