Remember how much complains we have when so many iPhone 3G users upgraded to iOS 4.0? It lags like hell when I upgrade my iPhone 3G to iOS 4.0, and have no choice to downgrade it back! iPhone 3G running iOS 4.0 is almost unusable! Slight improvement when Apple release iOS 4.1, but it seems like iOS 4.2 really fix the issue, and it seems to run very smoothly, of course you can’t compare it to iPhone 4.
But check out the video from TipB below, it seems like iPhone 3G users should really upgrade to iOS 4.2 if you wish to have the power of multi-tasking and folders, but don’t wish your phone to lag like a Windows Mobile Phone.