iPhone 4-S, upgraded for work reasons. Performance is slightly down, not as instant as before. You don't really notice it day to day, but it's there.
Is worth upgrading? Probably not, the much muted control centre and such has been available since I've upgraded. Times I've used it? 0.
That said I don't listen to music on my phone, if I did perhaps I would use features?
Have to say, the lock screen is a step back. I cannot find options to customise front size for lock screen, why would I want that? To fit more mails on it. With iOS6 I could see multiple alerts on lock screen without scrolling, at least a few e-mails and a text. Now? Just a single item!

Yes I have set font size to smallest, which works in say browser/sms but lock screen is bit shoddy really.
Search feature? Nice change, is it worth upgrading? No.
Browser is a nice update, bit cleaner, appears to "slim" everything down when scrolling. Auto hides back buttons and such, but find myself wanting them, but not displayed. So have to scroll up fast to trigger them.
Icon's are fresher, but I prefer Job's approach to realism. Flat Icons are a little dull...
Calender? Well that's better, but just basic improvements.
Photos? Well that's sorted better, by date time/location. Do I need this feature? Doubtful. Pano's and movies have their own section, but i could tell those apart before.
Battery life? It's the same, I feel everyone who says it worse is because they are using this shinny new OS more. Once they settle back to "normal" use, and an update as come out (7.0.1) suddenly the issue is fixed

Apparently some of the GUI affects are disabled on everything but 5-S, which we have arriving today apparently. So will compare.