Safari launch goes from 1.25 to 2.16 seconds, and I use that all the time. Not worth it, as much as I'd like 3rd party keyboards and 1password integration.
Plus there's the fact that everything is being designed for iPhone 5 and iPhone 6 screens now, so it gets terribly cramped without the extra height. Integrated apps like Music have already been crammed into the 3.5" screen on iOS 7, but 8 only takes more steps toward needing a bigger screen.
http://arstechnica.com/apple/2014/09/ios-8-on-the-iphone-4s-...