iPhone iOS 4.0 Upgrade slows down 3GS? Learn how to improve the performance

A few weeks back I upgraded my iPhone 3GS with the latest iOS 4.0 version. Initially it was uber fast and I enjoyed the new additions, especially multitasking. Now, I can keep my RunKeeper app and also work on other apps while I'm walking/jogging/running.

But, over the last few days, it has been very slow. It was painful to even compose a simple mail and to read emails. The solution I found is very simple.

1. Open the multitasking taskbar by double clicking the home button. (Pic1)
2. Click on the icons for a few seconds before they start shaking. (Pic2)
3. Close the apps which you no longer need to be running in the background by clicking on the red - (minus) sign on the left top corner of the icon. (Pic2)
4. After you've closed all the applications in the background, delete all the unwanted songs/videos in your iPhone using iTunes.

Hope that helps!