Now it is almost certain that Apple will release OS X 10.6.5 at the same time or even before iOS 4.2. Earlier we reported that iOS 4.2 went gold and is expect to be released in a weeks time-frame. Now 9to5Mac reports that Apple has already released the OS X 10.6.5 update internally in the Apple head quarters. OS X 10.6.5 update improves reliability with Exchange, resolve delay between print jobs, iPhoto improvements and more. The leaked list does not mention any preparations for iOS 4.2 interoperability.
The final 10.6.5 release is according to 9to5Mac the build (10H568) developers got on Halloween.