I read the arstechnica page discussing performance on the 4S before installing, but I really feel people should be more suitably warned! That review, and probably others, could easily be down played or totally ignored. It's not just a case of apps taking 30-40% longer to load, everything is slower and certain operations are at least 2 or 3 times slower. I performed an upgrade via iTunes and did a forced reboot after the install, so I don't think this is just a switch off and on again affair. Nor do I feel it needs to settle in. - Safari struggles to keep 1 page loaded. Previously I could have at least 1 or 2 'intensive' sites open in tabs, now it often won't open a SINGLE page. I had to quit all apps and quit and relaunch Safari just to view Macrumors home page. - Again, with Safari, once it starts loading a page it takes a huge amount of time longer to display. Loading Macrumors on iOS 7 took maybe 5 seconds, before it all displayed fluidly. Now, it takes 10+ seconds to get the first story to display and another 30 seconds to load the rest of the home page. I am not over emphasising/exaggerating. - Mail is about 2 times slower. Refreshing google inbox takes about 5 seconds, where as before it took 1 (almost instant). My work email (exchange) took about 30 seconds to refresh (check for mail...) rather than 1-5 seconds. Going to any inbox displays an empty page with line breaks for about 3 seconds rather than being instant. - General GUI/navigation is much slower. Coming out of standby is noticeably choppy and the iPhone will 'pause' after entering passcode. I suspect I will discover more slowness as I go. I am not sure at this point if there is a serious bug/memory leak that could be fixed, Apple have purposely introduced delays/lag to force an upgrade or if this OS is genuinely much more demanding on RAM/CPU. I am so glad I have an iPhone 6 on the way, otherwise i'd be pretty pissed off at this moment. Yes, I get that Android handsets often don't even get the option to upgrade (my gf has a 10 month old HTC that can't have KitKat) but I really feel this one should come with a warning or perhaps shouldn't even be available for the 4S.