Avoid the iOS 4 upgrade for the time being.
June 22, 2010
Our advice for upgrading to iOS 4 on Apple 3G 3GS and iPod is to aviod it for the moment. There have been quite a few upgrade issues so let the dust settle and wait for the next minor version release.
And before you do proceed, make sure you get a complete backup. News from the Apple forums reveal too many failures when trying to restore.
Even PC Pro see has reported on this issue.
Some people have already said that the upgrade is just not worth it because it slows down the device and many applications are not multi-tasking aware.
In order for mutli-tasking to work, the application has to be aware and many of the 225,000 apps have not been amended. This is not directly Apples fault. However, the developers only got notified of the update last week so have not had sufficient time to make the changes requirement and resubmit the app for approval.