It is an improvement over 8.0 but not over 7 in terms of speed. If you don't need or want anything from iOS 8, then stay away. I upgraded cause I'm moving to a 128 6+ in a few weeks.
If you're expecting speed to improve in the 4S, that's nowhere in the horizon. This phone is 3 years old and it served its purpose already. I'm an owner of a 4S and I'm expecting this but it did not stopped me from upgrading to iOS 8. As long as it did not brick my phone, I'm good with it. What really made me switch is the Extensions feature allowing third party applications to be used together with default iOS features (shared this post in the iOS 8 thread for Evernote). I'm on iOS 8.1 today and I'm still good with it. As Hero33 mentioned, if you don't need any feature from iOS 8 then don't upgrade.
I'm also on ios 8.1 on my 4s. I don't regret updating the ios. To each his own i suppose. Other than call and text, i tend to use my ipad more. I'm glad i can do that too on ios 8.1.
In your 4s with ios8.1, does your apps crash more compared to ios7? I'm afraid I can't open some of my apps.
What apps do you usually use you? Haven't encountered any, i think. I pretty much only use call, texts, email, safari, spotify, tapatalk, dragonvale, synology apps and a few others.
Just to add up in this topic, try to read this. iOS 8.1 iPhone 4s Reviews: Should You Install iOS 8.1?
I updated my 4s 64gb to ios8.1 and it is working great! Swiping from the home screen has no lag. I tried opening Safari and Clash of Clan and its performance is the same with ios 7. The only thing that is slow is the upgrade itself. And upon startup of new ios8.(Where you will be ask to configure). With this, I can suggest you guys to upgrade yours too if you need the new features of ios 8.
Regarding app crashes, they crash a lot when I upgraded last year to iOS 7, its more stable in iOS 8. I'm on iOS 8.1 already, 4S and iPad mini (1st gen).
Haven't upgraded to 8.1 on my 4S. It's still good and I don't know any of the new apps on 8.1 that I may need. What I don't see won't attract me, hehehe..
My mom's 4s (iOS7) photo stream isn't showing up on her iPad Air anymore (iOS8). Should i update her iPhone to iOS 8.1 too?
I was satisfied when i upgraded from ios7 to ios8.1. Will try to upgrade to ios8.1.1 today and will inform you guys if it's better. FYI:
No need to wait for his feedback. My 4S and iPad Mini is working flawlessly and snappier after the 8.1.1 update.