I've upgraded to iOS7 on my iPhone 4s. The keyboard, regardless of what I am doing, either texting or entering email, is extremely sluggish - 5 second interval between keystrokes.
What are some ways to troubleshoot this problem?
Try turning off "Documents and Data" in iCloud. It should make typing faster. You can turn it back on, but if you go to iCloud Storage and Data, it will start lagging again. You then must turn off "Documents and Data" once more.
This info was in the comments of this review: http://www.gottabemobile.com/2013/09/18/ios-7-iphone-4s-first-impressions-performance/
I am going to attempt this on my iPad 3 and my iPhone 4 since they both are clearly slower at responding to keyboard input on iOS 7 than they were on iOS 6. I half expected the iPhone 4 to my laggy the first few days and it it. I wasn't prepared for the iPad to stutter so much.
Here is what I've learned:
My backup that I loaded was slowing the device down a little, but much of the slowness persists when I erase all content and settings.
This happens on both the iPhone 4 and iPad 3. It's not horrible once the OS is done getting all the pop up messages, apps updated and things generally settle down. For the first few hours, my typing was definitely getting truncated. Passwords I've typed hundreds of times (and thus quite quick) would miss letters and be rejected initially.
After a night of charging and all the apps updated, the iPad has all the apps from an iCloud restore and all the settings intact. The iPhone 4 erased all content and settings and have only enabled a few things like iTunes Match, podcasts and mail accounts (iCloud x2, Office 365 x2, IMAP) and the usual Messages, FaceTime, and core apps that ship with iOS.
I plan to see if iBooks and the rest of things slow down the iPhone 4 too much for me and make a call next week to sell it / keep it at iOS 6 or tough it out on iOS 7 in hopes that some or all of the "slowness" gets tuned away.
I do expect Apple to get a lot of real world metrics from bar appointments, troubleshooting logs and misbehaving app crashes to get things tuned up better - but that doesn't help me today. Sometimes, but not all the time, the keyboard is lagging half a beat or more when it did not used to nearly as often.