i heared Apple put in some features to speed up things but are not turning out so well.
eg when you first startup your iphone/ipod, unlock it and then slide the screen to the right(to go to the search screen) you will notice that the screen does not slide smooth but freezes half way and then pops up the search screen.
They tried to save some time but in fact EVERYBODY is experiencing this as a lag in the screen, thus it is SLOWER.
there is a tool you can download in Cydia which says it speeds up things but the only thing it does is get rid of this buggy feature that apple introduced.
bumer for us is that we need to jailbreak the device to use his tool.
i agree, Apple should fix things.
the reason why i still did not jail break the device is that i thought it is more stable with the original fw.
now that it is not i might try cydia to see if things get smoother
even my 3gs is faster than my iphone4 at the moment