Everyone whined about wanting multi tasking. I don't know that I like it. Now I seem to be constantly worried about going into the task switcher and closing things that I don't want to still run, worried about battery life. I haven't had a full day of use yet, but we'll see how the battery does without intervention in the task switcher over the course of the day.
According to Jobs, you don't need to worry about closing the stuff. Just let it be, it'll handle itself.