So this naming thing. Small thing in light of today's announcements, but still...
Why "OS X"? What's with the X? I never saw anywhere that this is officially Mac OS version 10.9 regardless of the previous version's number.
There have been two operating systems for Macintosh: MacOS, with versions from 1.0 to 9.0 (or maybe 9.1, feel free to check Wikipedia), and OS X, with versions from 10.0 to 10.8 released, and 10.9 just announced. The name OS X will be kept until there is a substantially different operating system (and by substantially different I mean something that is much more different than iOS, for example), which will probably not happen for the next 15 to 20 years.
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2) Version numbers are not decimal numbers. For one thing, they have multiple decimals (eg: 10.8.3). You can go from 10.9.4 to 10.10.0 to 10.11.0. There's no need to bump the major version from 10 to 11 just because you've already used 9 for the minor version number.
There was a version 10.4.11, so there is precedent for this.
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It says right there that Keychain is moving to the Cloud. Meaning to me it is no longer on your computer.
Scary.
Your interpretation is scary. But so far, everything that is stored "in iCloud" is also on every device that sync'd to it, and on the device where the information was created. So if you create a password on your Mac, it is on the Mac and stays there; it is also copied to iCloud, then copied onto an iOS device or second Mac when needed, _and stays there_.
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That means my wife's MBP is supported. Surprised, as I would have expected Core2Duo support to be dropped in 10.9.
There's no reason to do so. Core Duo which was a 32-bit only processor was dropped in 10.8, which has the huge advantage for developers that apps written for 10.8 only can assume there is a 64 bit processor, and they can assume that certain modern OS features are available (which were missing on 10.7 in 32-bit code). With Core2 Duo, there is really no justifiabie reason to drop it at the moment.
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Looks like there may be lots of potential problems with this version:
You just posted a ton of information that is under NDA, and only intended for people who right now can legally install 10.9 pre-release versions (in other words, developers). Anybody who has legitimate interest in this information already has it. So if you tried to make yourself appear clever, then you failed miserably.