The seed, true to predictions earlier in the day, is indeed build 10A314, which arrived in tandem with an identically labeled build of Mac OS X 10.6 Snow Leopard Server.
According to people familiar with the matter, Apple is "strongly encouraging" developers to get busy developing and testing 64-bit support in their kernel extensions (typically low level hardware drivers) for the new build.
While relatively few third party developers create kernel-level software, the new operating system won't work in 64-bit if users lack 64-bit versions of the kernel extensions (kexts) they need.
Developers can deliver both 32 and 64-bit kexts that will enable Snow Leopard to automatically boot as a 64-bit kernel on 64-bit hardware, including all Macs that use a Core 2 Duo or Xeon CPU, while also working properly in 32-bit on earlier Macs using Core Solo or Core Duo CPUs.
Microsoft faced similar driver transition issues when it tried to move Windows XP users to Windows Vista, which used a new driver architecture. Windows users have also faced some transition problems in moving from the 32-bit versions of Windows XP and Vista to the 64-bit versions of those operating systems.
Apple's need to get kernel developers up to speed on 64-bit support is somewhat less problematic because Mac OS X runs on a much smaller subset of hardware than Windows does, and Apple develops or manages most of the kernel-level driver software that most Mac users need to use the new 64-bit kernel.
Users who have specialized hardware and want to run Snow Leopard in 64-bit will need to make sure their vendors supply them with 64-bit versions of those drivers by the time the new operating system ships; it is expected to be released sometime this summer.
Other software faces less urgency in moving to 64-bit, as the Snow Leopard 64-bit kernel has no problem running 32-bit software outside of the kernel; it just can't run 32-bit kernel drivers. Other 64-bit processes similarly can't run 32-bit plugins or extensions, so developers of "pref pane" modules that get installed in System Preferences will need to release 64-bit versions of those items to allow users to run the 64-bit version of System Preferences.
The Cupertino-based Mac maker is also reportedly equipping developers with a new 64-bit transition guide to make the process as smooth as possible.
Other change arriving alongside the new build are an updated version of Xcode and the ability to install Snow Leopard on MacBook Airs wirelessly via Remote Install, those familiar with the matter say.
As was mentioned earlier, it appears Apple will hold any cosmetic changes to Snow Leopard's interface from the public until its annual developers conference in June.