MITES 09!
Don't be afraid because of the stats- they really are looking at you as a whole instead of numbers. (And it worked, we had a great group)
I had 3.9ish GPA/4.0, don't remember the exact PSAT subscores, but it was 215 total, and my school ECs weren't too special, but I did start my own small business over the internet.
Basically, here's what we covered in my classes:
Calc 2:
From vectors through double and line integrals of multivariable functions and basic differential equations. We covered most of what you would get in 18.02 at MIT, actually. It was pretty fun.
Physics 3:
God, this class made my brain explode daily. We started with a mass on a spring, added friction and a driving force, made it 2 masses, then 3, then n masses, then infinity masses, then zoomed out and called the masses atoms and we were just barely starting quantum by the end of the 6 weeks. It was intense. This was equivalent to 8.03 at MIT
Biochemistry:
We started at amino acids, worked through DNA, RNA, and proteins including their structures. The class was interesting, but not as intense as Physics or Calc for me. Lots of memorization, including all the structures for amino acids, etc.
Humanities:
We read 4 books and discussed in class. Some people pretended to read 4 books and discuss in class, but that wasn't the best strategy. The class was divided in half: 1 half racial issues: Books were: Obama's Dreams from my father (interesting, but very very dense and slow reading) The absolutely true story of a part time native american (a fun, light read)
and 1 half science and morals: Copenhagen (I found it interesting, some people disliked it) and Saturday (The slowest read ever! 30 pages to narrate the main character getting up and going to the window. It gets quicker later on, but it starts off so slow that I had trouble making myself read it.)
We had to write two papers (5ish pages? I can't remember) and a few short 1 page responses.
Engineering design:
Build a robot that competes with other robots to do things. It was not much work, until the last night, when we pulled an allnighter. It was pretty fun. (Nicoliolioli really really loved it...

)
A sample MITEs experience: You had your physics PSET due today, so you've slept about 3 hours and haven't started on your final essay. You get to the dorms after school, eat (the summer food at simmons is horrible, by the way, more at the end), and are told that everyone has to watch a movie today at 8:00 (minority report) because it's part of the science and technology issues. You get done and back in your room by 11:00, and then you have to start your final paper.
Then, to make things worse, I know some people had to read the books, and THEN start their final papers.
Looks like another allnighter. But it's not so horrible, because you go to the lounge and work next to friends in the same situation as you, and you all take a small break to watch the sun rise, and then keep working on those papers.
It's intense, but not so bad because you're with others.
Food at simmons is served sun-thurs dinner. It is horrible. They can't cook spaghetti, burgers or hotdogs (and even I can make a hotdog, so it isn't that hard).
We got $70 a week to spend on breakfast/lunch and weekend dinners. Most people had it last them pretty well, unless they brought too many snacks and junk food for PSET groups.
Summary for the people who skim long passages:
You will do allnighters.
You will feel bad when you get your midterm grades. (Class average in physics 3 was a 19 percent. That was a doozy.)
You will improve, and become much better than you thought you could be. (Class average at the end of physics 3 was actually passing, so we almost quadrupled the average grade. The best improved guy went from an 6% to a 98% on the final...)
If I could do it over this year, I would in a heartbeat. So yeah, apply.