I only see one post in the 100 section, so as a 100 rider myself, I feel I need to speak about the bike.
My first dirtbike was a KX500. I liked it alot, but it was way too much bike for me at the time. I used to weight about 150lbs when I got it and I got a pretty bad injury when riding (not to mention a scar on my foot from slipping off the kicker when starting it).
So I sold it and got a new 100. I love the bike. It is rediculously light and really has a lot of power. My 12yr old brother has a 2002 YZ85, and even though I now weight about 170(going to the gym), I still rip him in drag races and my bike is just way faster (although he is a much better rider than I am).
But now I'm so happy because I will be getting another 500. I loved how much power the 500 had. I can't wait to ride one again. I should have it in 2-3 weeks