Yeah, the year before my first kid started kindergarten, our district switched to a calendar that runs 9 on/2 off/9 on/2 off/9 on/2 off/9 on, which leaves 8 weeks for summer break.
This is the way I look at it: Everybody else is taking family vacations from July 30-August 12 while my kids are in school. We can take family vacations from October 4-17 while everybody else's kids are in school. Hotels are a little bit cheaper and popular tourist attractions will be less crowded.
We're actually coming up to Chicago the week of October 11. I expect the museums to be much less crowded than if we were there right now.