When I updated my iPhone 3G to iOS 4 a couple of weeks ago, I didn’t experience all the performance issues many people pointed out. I could feel some slowness at times, but nothing remarkable, and the iPhone has always been usable. The only glaring exception was the iBooks app, sluggish and hardly responsive, to the point of being frustrating and ultimately useless. (By the way, I still think the best iBook reader on the iPhone is Eucalyptus.)

Still, the various horror stories I was hearing about this apparent disaster that iOS 4 has been for iPhone 3G users, made me wonder. What could be the reason for such different problems on basically the same hardware? The update process was the same for everyone: connect the iPhone to iTunes, download and install the firmware update, patiently wait an inordinate amount of time, until after a final sync the iPhone was ready to be disconnected.

It had to be something that’s as differentiated as the issues themselves. Configuration, perhaps, since probably there aren’t two identical iPhones out there as regards to number and kind of applications installed. So — not being a developer but just a power user — I ventured a guess: performance issues in iPhone 3G with iOS 4 might be related to how many apps are actually optimised for iOS 4. A lot of things have changed under the bonnet from iOS 3.1.3 to iOS 4, so perhaps all the apps that aren’t yet recompiled & optimised for iOS 4 are giving iPhone 3Gs [plural of “iPhone 3G”] a hard time with memory and resource management. Hence the sluggishness and poor performance.

These past days I witnessed something interesting on my iPhone 3G. As more and more apps were updated and made iOS 4‑compatible by their respective developers, I couldn’t help but notice (wait for it) a progressive performance improvement. The iPhone keeps feeling snappier. Transitions and animations are smoother, more apps seem to open a tad faster than before, the virtual keyboard feels more responsive, and (again, wait for it) the iBooks app itself has mysteriously improved to the point of being actually usable.

I haven’t done anything special, nor I’ve tried some of the suggestions I read on the Web to try to make the iPhone 3G more responsive under iOS 4. I haven’t restored it, I haven’t reinstalled the firmware, I haven’t force-rebooted it, I haven’t reset all settings. I just synced it two or three times in the last ten days or so. (Oh, the backup/sync process has definitely improved with iOS 4, by the way. Now it’s ridiculously faster than before — 3–4 minutes against the 25–30 minutes under iOS 3.x).

So maybe my guess was not too far-fetched. If you’re still having performance troubles with your iPhone 3G under iOS 4, try checking if you have some particularly crappy apps that haven’t been optimised for iOS 4 yet. An ideal thing to try would be to keep track of all the apps that have been updated to support iOS 4 and temporarily remove all the others from the phone (they remain in iTunes, although you’ll probably lose their data and settings), restart the phone and see if performance gets better.