No wait, if there is a task killer then you blew it! lol.
THere IS a task killer, and no, you don't need it. The OS should be smart enough to manage the memory. Android is. I assume iOS will be.
What Steve Jobs said was, "If there is a task manager then you blew it." and that refers to the sort of thing that was on LG phones. Not the iPhones list of recently opened apps (which is all it really is) It is not equivalent to a task manager, the sort of thing you see in Windows with alt-ctrl-delete.
EDIT: Exact quote: "In multitasking, if you see a task manager, they blew it. Users shouldn’t have to ever, ever, ever think about that stuff."