As Apple began selling the new iPhone 5S and iPhone 5C to customers this morning, iOS 7.0.1 was also rolling out to all the newly activated iPhones.
The minor update, simply lists "bug fixes and improvements" as the payload for this update. My guess is these are just last minute tweaks for the new hardware. The update is just 17.6MB.
Apple is also said to be working on iOS 7.0.2 and 7.1 already according to the usual "people close to the matter".