It works better than I ever expected. Same performance as in iOS 6. So yeah, it stutters a little sometimes, but extremely workable and looks fantastic. I'll definitely hold out until the iPhone 6 now.
I have a 4S, which I know is faster than a 4, but same overall experience here: iOS 7 equivalent to iOS 6; I don't notice any performance degradation in regular and even stressed use. I was going to get a 5S though in theory I prefer to wait for whole number releases because of, minimally, the gee whiz points of a new or greatly revised form factor -- yeah, like I did with the 4S; but my 4 was stolen so I have an excuse on that one. But I've got this Speck 4S case with the PRC flag on it, a case that still has a year of rugged use left in it. I didn't get in China. I got it here. I'm not sure it was ever intended to be sold in the States, but I found it for a few dollars in a discount store and the irony of an iPhone in a case with the PRC flag on it is just too much to let go quite yet. Besides, I like the uniform materials of the 4 and 4S. Glass front and glass back. I know, I'm going to have to give that up at some point but I'd rather not for another year.
My general policy on Apple upgrades, if you can at all wait, do so. The new model may not be much better, aesthetically or technically, but it's highly unlikely that it'll be any worse. And if you like toting around the latest and greatest form factor, it's hard already to tell a 4 from a 5 unless you look for the Lightning connector. That won't change much if any for the 5S, unless it's a gold and you'll have to wait for that and you'll likely stick it in a case, anyway. So if you wanna be all fly and stuff -- and really, who doesn't -- and you have a 4 or 4S, by all means starve Apple's annual revenue and wait the iPhone 6.
P.S.: I did an over-the-air update and still there are no performance issues. As far as I can tell there's not much to delta in the iOS 7 update; it's pretty much the whole OS whether it's OTA or via wire + iTunes.
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Maybe I need to get used to iOS7 more and on a fast iPhone 5/5s?
If you already can't find things in iOS 7, I'd think faster would make that worse.