According to user reports, when installed on the iPhone 3G, iOS 4 runs sluggish as compared to running on the 3GS and iPhone 4. Of course, the over clocked processor speeds have been taken into account but the reported performance decrease is nothing to be overlooked. In fact, Apple came forth to announce that they are aware of the problem and are working to develop a fix for the problem. How to fix this?
Go to “Settings -> General -> (Home Button – only 3G) -> Spotlight Search -> deselect every option”and this will stop background indexing on the phone. If you do decide to do this, be sure to tell me how it goes because it would be interesting to see if this is actually part of the problem.