Last night I loaded iOS4 on my iPhone 3GS...
I like that I can add more then one Exchage account to my iPhone.
I like that I can make folders.
That is about all I like.
The mulitasking is strange, because it seems like everything is running after you close the program. When you double click on the home button you get a list of all the programs that are running and it shows every program I ran and stopped.
For multi media programs there is no program released yet which can multitask. So when you click the button to exit the program the music stops... (but the program shows up in the multitasking list.)
So far its not that great of an update.