Since I live here in Derby City, let me give you the low down on some details for the July 14th concert. (That means you Dive!)
If you are driving here, you need to know that I-64 in downtown Louisville is closed right now, which is the main artery into the city from the West. Make sure you take I-264 to circumvent this if you're coming from the west of town (Take the Taylor Blvd or Crittenden Drive exit and go North).
As far as parking goes, it could be chaotic. The parking lot at Churchill Downs is small for an event of this magnitude. A good option is to park at Papa John's Cardinal Stadium (less than a mile away, huge stadium) and ride the provided bus service to the Downs. Although I'm not exactly sure how traffic will be routed on Saturday...
The final issue is the weather, as this is an outdoor event. Luckily I have a good background in meteorology, so here's my forecast for the concert:
Clear, mid 70's.
This is a little thorough I know, but I don't want anyone to get stuck in traffic during the greatest show on Earth!