Amanda Baggs wrote a great article which I recently read and recommend that you do too. It brings up the point that defining "high-functioning" in Autism Spectrum Disorders is incredibly difficult. Most of those on the spectrum have areas which they excel in and areas which they are very weak in. Classifying someone as high-functioning just based on one or two characteristics is difficult, as is classifying the same person as low-functioning. Nearly all of us have something which we're amazingly good at or can be seen as high-functioning in as well as things which would have us seen as low-functioning.
I am able to attend college and live on my own without support from any kind of aid. Am I high-functioning?
I have breakdowns where I lose the ability to speak and can only scream and hit people. Am I low-functioning?
I can write and speak fairly eloquently and have a large vocabulary. Am I high-functioning?
I become upset and will lash out or cry if my routine is interrupted. Am I low-functioning?
If you just look for high or low functioning, you're going to get pretty confused. I, for the most part, am very high functioning, able to hold a job, attend college, have friendly and intimate relationships and advocate for myself. However, that doesn't mean that I'm no longer autistic. I stim, bite myself, spin things, need lists, schedules and order, cry or laugh seemingly without reason and have terrible breakdowns - all things which point to autism.
The truth is that labels like "high-functioning" or "low-functioning" are very subjective, unscientific terms. Every person will present their symptoms differently. Alecta's autism is not Julia's autism or Chris' autism, even if we all have Aspergers. While it might be good to give someone a general idea of how severe symptoms are, it won't give an idea of what skills are already there or what challenges someone faces. The fact that I'm considered high-functioning doesn't dismiss the challenges I have in my life.
I don't know how we could more accurately label autism other than being specific about individuals. We've come a long way from thinking of autism as a form of childhood schizophrenia, but we still have a long, long way to go before we can really accurately describe what is going on.