iPhoneHellas.gr is claiming they've heard Apple will release iOS 4 later today. They've gotten that kind of stuff right before, and Apple does have an iPhone 4 press conference scheduled for tomorrow, so the timing would make some sense. iOS 4.0.1 being released would mean the changes to the way bars are shown and reported in the developer beta for iOS 4.1 would be public and could be stated as such by Apple.
It would be a couple weeks earlier than Apple's usual end of July/beginning of August iOS x.0.1 update cycle, but likely welcome by those suffering proximity sensor issues and other iOS 4 bugs.
Ping us if you're iTunes catches an update.