Our own experience bears this out.
Regular TechRadar writer Gary Marshall upgraded his iPhone 3G to iOS 4, and had this to say:
"Upgrading killed my 3G: the screen doesn't always respond, apps take an eternity to launch and some are so slow they're unusable. It's now quicker to walk somewhere than look it up in Maps, and the iPod app and SMS app take forever to open up. Worst of all, I can't always swipe the screen to answer a call.
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"I don't know if it's a coincidence but I'm also getting terrible network coverage too. I'm going to try a wipe and clean install in the hope that that fixes it, but the download servers are getting hammered and it's looking like that'll be an all-afternoon job. I wouldn't mind, but I've already wasted several hours upgrading in the first place. I'm having Windows 95 flashbacks here."
And TechRadar editor Patrick Goss, who also recently upgraded his iPhone 3G, said:
"I was delighted about getting the latest update - especially given the news that original iPhone owners were being left behind - but I'm really wondering why I bothered. The phone was already feeling a bit creaky when I wanted it to actually open something, but since I moved to iOS 4 it has got even worse. Given the choice, I would probably downgrade back to the prior operating system."
We want to find out how widespread this issue is, so if you've recently upgraded your iPhone to iOS4 please let us know in the comments whether you've found that your phone feels slower after upgrading.
When commenting, please mention whether you have an iPhone 3G or an iPhone 3GS.
If it doesn't feel slower, please comment and let us know that, too.