President Barack Obama is scheduled to address the nation live regarding Afghanistan this Wednesday at 8pm ET, and it looks like ABC, CBS, Fox and NBC will all carry it live.
While it's easy to say "who cares, summer is all repeats on the broadcast networks!" that's only true on Wednesday night for ABC and CBS.
NBC's will have to make accommodations for "The Voice" and "America's Got Talent" and Fox for So You Think You Can Dance. For now it looks both networks will just move the start times for the regularly schedule programs and run past the end of their normal primetime blocks. If that changes, I'll update this post.
Update: it looks like the address is only planned to be around 10 minutes, so the schedules will just be pushed ~10 minutes.