I have run through two crazy hot summers with outrageous humidity levels. I learned that no matter how often you practice running in the heat, it doesn't make it any easier or safer. Becoming dehydrated or over-heated is always a possibility. The difference is that someone used to the hot weather would notice the symptoms that tell him or her to slow down or take other preventive measures to maintain a healthy condition.
The decision to cancel the 13.1 Chicago race was an appropriate one and might have saved some lives.
As I did last year, I plan to get up around 4 A.M. to go out for my morning run. It is a beautiful sweaty run and has to be done at no more than 80 persent power. The only disadvantage is having to go to bed early at night when it hasn't cooled down properly yet. It takes a while before being able to fall asleep but it feels great to wakeup when it is warm.
Throughout the day I have to keep an eye on my water consumption and the amount of electrolites (from salty food) I get inside me. But I love it, even though it is tough it is way better than winter.