Lots of little fixes that will make life on an iPhone 4 better. In addition to all the items covered in the linked article, I also found Bluetooth syncing to be much more solid on our test phone. For example, with iOS 7.0.x, the music app in a Bluetooth connection stuttered frequently. With iOS 7.1, things are noticeably better.
iOS 7.1 a noticeable speed improvement on iPhone 4
Where’s Catherine Rampell now, the author of this little gem of an article? http://www.nytimes.com/2013/11/03/magazine/why-apple-wants-to-bust-your-iphone.html
Not just the 4. My 4s feels… dare I say it… peppier. The animation speed was abysmally slow before and now it feels 2x as fast.