"For those with access to the (iTunes) 11.3.1 installer, you'll notice when running it (by selecting "Installer Log" from the Window menu and setting the Detail level to "All Logs") that a number of components are skipped "because the version [newer] is already installed."

In order for all of the 11.4 components to be replaced, in addition to /Applications/iTunes.app, you will need to remove:

/Library/Frameworks/iTunesLibrary.framework
/System/Library/CoreServices/CoreTypes.bundle/Contents/Library/MobileDevices.bundle
/System/Library/Extensions/AppleMobileDevice.kext
/System/Library/Extensions/AppleUSBEthernetHost.kext
/System/Library/PrivateFrameworks/AirTrafficHost.framework
/System/Library/PrivateFrameworks/CoreFP.framework
/System/Library/PrivateFrameworks/DeviceLink.framework
/System/Library/PrivateFrameworks/iTunesAccess.framework
/System/Library/PrivateFrameworks/MobileDevice.framework

Having done that, and re-running the 11.3.1 installer, the buggy 11.4 version will have been removed and 11.3.1 restored.
-cwa2"

There have been many problem posts on iTunes 11.4 (see earlier FYI below). I don't know how many had or tried a restore from TM backup instead of the above. But posting it regardless as it has been useful to others that regretted installing iTunes 11.4 and found reinstalling 11.3.1 didn't help due to later files not being overwritten by the older iTunes installer.
  

"About iTunes 11.4
(link disabled as same page URL is used for later iTunes updates)
iTunes 11.4 now supports the ability to sync your favorite music, movies, and more to devices with iOS 8.

File Size: OS X (242.92MB), Windows (111.3MB), Windows64 (112.8 MB)

System Requirements:
- OS X version 10.6.8 or later
- 400MB of available disk space
- iTunes in the Cloud, iTunes Match, iTunes Radio availability vary by country
- iTunes Radio requires OS X version 10.7 or later
- iTunes Extras requires OS X version 10.9.3 or later"

FYI: There's several threads in Apple's forums about an AppleUSBEthernetHost.kext (extension) related error message after updating to iTunes 11.4:

"System extension cannot be used
The system extension "//System/Library/Extensions/AppleUSBEthernetHost.kext" was installed improperly and cannot be used. Please try reinstalling it, or contact the product's vendor for an update."

Example thread links, some with tips (usually deleting the extension and then reinstalling iTunes from a download installer (link above):

• System extension cannot be used AppleUSBEthernetHost.kext
• Post w/info on AppleUSBEthernetHost.kext versions and symbolic links
• AppleUSBEthernetHost.kext error on installing iTunes update
• "System extension cannot be used" after installing iTunes 11.4

I later noticed one post said AppleUSBEthernetHost.kext does not support 32-bit anymore. (Some had said deleting the extension and then reinstalling iTunes 11.4 using the Download installer didn't help on their system.) (Update: See later tips above on reverting back to iTunes 11.3.1.)
  

• Keynote Video of Apple 9/9/2014 iPhone 6/Watch event
• iPhone 6 product page
• Apple Watch product page
• Apple Pay product page
  
  Press Releases:
• Apple Unveils Apple Watch - Apple's Most Personal Device Ever
• iPhone 6 & iPhone 6 Plus - The Biggest Advancements in iPhone History
• Apple Announces Apple Pay (Mobile Payments)
• Apple Announces iOS 8 Available September 17
• Apple & U2 Release "Songs of Innocence" Exclusively for iTunes Store Customers

BTW: Threads in iTunes forums on problems downloading the free U2 album (Can't download U2 "Songs of Innocence", Songs of Innocence not in library? & Free U2 album) include tips.
(Update: Despite the above posts, apparently Apple received enough complaints from users that didn't want the 'automatic' free album that they posted a URL to remove it from your iTunes library and purchase history. See https://itunes.com/soi-remove.)
  

• Identifying iPhone models (added iPhone 6/6 Plus)
• Vintage and obsolete products (added iPod classic)
• AppleCare+ for Australia (unknown changes)

(Topic-based page of Tips, Troubleshooting & How-To Guides for Mac/OS X/iOS Users.)
  

• Apple iPhone 6 analysis (EDN)
• HGST Announces 10TB SMR HelioSeal™ HDD (HGST)
• Netgear Nighthawk X4 review: A disappointing 'Wave 2' effort (PCW)
• Google Chrome 37.0.2062.120 (security update) for Mac/Windows/Linux
• Adobe fixes critical flaws in Flash Player, delays Reader and Acrobat updates
• VirtualBox 4.3.16 (Change Log includes a few OS X related.)

Monday Sept. 8th, 2014 News
• Apple's Low-Cost Business Mac: PC Implications
• 24bit/192Khz audio over HDMI with (late 2012) Mac Mini not supported? (OS X)
• Sapphire Screens Would Test Apple's Manufacturing and Design Skills
• GeekBench 3.2 released
• PCIe SSDs: Samsung XP941 vs OCZ RevoDrive 350
• Creative Labs (USB) Sound Blaster X7 preview
• Carmack talks VR gaming's past, present and future
• Intel Xeon E5 version 3, Up to 18 Haswell EP Cores
• Review of Epson Expression Premium XP-520 ($130)

For links to older news pages, see the Archives.