Sources internal to Apple have informed 9to5Mac that OS X 10.6.5 has been finalized and circulated within the company. 9to5Mac also notes that such pre-release updates "usually come in one to a few days prior to public launch."
10.6.5 is required for most AirPrint functionality in iOS 4.2. Since iOS 4.2 just reached GM status, it's likely a public release for OS X 10.6.5 will roughly coincide with the public release of iOS 4.2. Both OS releases are expected within the next week or so. We'll let you know as soon as they go live.