Check your software update panel ... I just installed it, and I'll post back details after I restart!
OK, here are the details. The modified files list seems to indicate that there have been changes to the BSD kernel, ADB I/O, CD storage, DVD storage, graphics I/O, networking, PCI, and a number of other areas. I've posted the whole list in the remainder of the article, in case you'd like to see it (it's not too long).
As for the operational changes, I can't say that it feels much different, but I'll have more to say after I get a chance to re-run my benchmark suite this evening. Apparently it squelches one bug in the Finder dealing with folders with large numbers of items. If you had over some relatively small number (600ish) in one folder, all the Finder would show was 539. They'd be there (you could see them in FTP or the terminal), but the Finder wouldn't work with them.
The following files are included in the update:
./System/Library/CoreServices/SystemVersion.bundle/English.lproj/SystemVersion.strings
./System/Library/CoreServices/SystemVersion.plist
./System/Library/Extensions/System.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/BSDKernel.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/BSDKernel.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/BSDKernel.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOADBFamily.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOADBFamily.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/IOADBFamily.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOCDStorageFamily.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOCDStorageFamily.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/IOCDStorageFamily.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IODVDStorageFamily.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IODVDStorageFamily.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/IODVDStorageFamily.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOGraphicsFamily.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOGraphicsFamily.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/IOGraphicsFamily.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOHIDSystem.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOHIDSystem.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/IOHIDSystem.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOKit.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOKit.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/IOKit.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IONDRVSupport.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IONDRVSupport.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/IONDRVSupport.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IONetworkingFamily.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IONetworkingFamily.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/IONetworkingFamily.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOPCIFamily.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOPCIFamily.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/IOPCIFamily.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOStorageFamily.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOStorageFamily.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/IOStorageFamily.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOSystemManagement.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/IOSystemManagement.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/IOSystemManagement.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/Libkern.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/Libkern.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/Libkern.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/Mach.kext/Contents/Info.plist
./System/Library/Extensions/System.kext/Contents/PlugIns/Mach.kext/Contents/PkgInfo
./System/Library/Extensions/System.kext/Contents/PlugIns/Mach.kext/Contents/version.plist
./System/Library/Extensions/System.kext/Contents/Resources/English.lproj/InfoPlist.strings
./System/Library/Extensions/System.kext/Contents/version.plist
./System/Library/Frameworks/Kernel.framework/Versions/Current
./mach_kernel
./usr/lib/libIOKit.A.dylib
./usr/lib/libIOKit.dylib
./usr/lib/libkmod.a
./usr/lib/libkmodc++.a
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