When the ios 8 upgrade notification popped up on my iphone 4s, it asked for almost 5GB of free space to install about 800mb of operating system. It took me a while to get 5 GB space but I did it after few weeks to deleting unnecessary apps and videos.

IOS 7 was working perfectly and everything was super fast. Apps would open right away and the responsiveness was just great.

Then i installed IOS8 and there was night and day of difference. Everything was slow. The responsiveness was not there. Sometimes it would take 10 seconds for the screen to acknowledge my touch. All apps are taking almost a minute before I can start using it. Even facebook app takes a while to load.

Let's trust these greedy tech companies to screw up a working product just because they need to sell their new phones.

Every higher version of OS is designed for new hardwares. So using latest OS with old hardware, there will be some slowness. Software cannot take full advantage of the required hardware. iPhone 4s has only 512mb RAM, and runs on A5 chip. And main difference is on graphics rendering.
Same thing happened with my Macbook pro when I upgraded last week to Yesomite. I have 2011 Macbook pro i7, which was running great until I upgraded. Now my 8gb ram will be completely used up even when I am not using any heavy apps.

So bottom line, if you don't want to buy new hardware, don't upgrade to new software. They are designed to work with new hardware.

I was going to say same thing, but on webjunkie's defense, iPhone should also release a statement stating the backward compatibility issue.

I have an iphone 5 and i didnt upgrade to ios 8.

It's so obvious these days that upgrading os will slow your phone down. There are reviews and videos all over web. Next time read about the new release before upgrading your os.

So much for your name 'webjunkie'

does this consider as an irony? i still havnt been able to grasp this whole irony thing. someone please confirm this. thanks. :)