picked up a white one yesterday! had iphones for 4 years, this is my first android! so far its soo good

battery seems reasonable just like iphone, and the screen is gorgeous!
now one question! as this is my first android, ive noticed under settings that you can check what applications are running etc via the application manager. on mine it seems that theres loads running taking up almost 3/4 of the memory. does this matter? it doesnt affect the performance from what i can tell but it seems weird.
i downloaded the task killer and as soon as i kill them, check bk a few minutes later and they are back so im sure thats pretty pointless worrying about?
as i say my first android, just making sure this is normal
thanks