I had fairly crooked, crowded, overlapping teeth that I was mildly self conscious about, but didn't want metal in my mouth at 25. That was for 12 year olds. ;) So, I just dealt with them. Anyway, when I heard about Invisalign when it FIRST came out, I immediately had a consultation, and the dentist told me that I was not a good candidate, as my teeth were too bad, and they'd have to break my jaw, etc etc.
Anyway, I waited a couple years, and then tried again with a different dentist. I told him I'd be happy if they were even 50% better. He said he could do 90% and I was THRILLED. I signed right up.
I've been in them for a little over 2 years, and my teeth are way better than I ever hoped for. My teeth are at least 90% better. I still have a narrow jaw, as they can't fix that without breaking it, but my teeth are all straight and my front teeth aren't overlapped anymore.
I am more than 100% happy with Invisalign, and I would recommend it to anyone.