Very good read on the facts about how iOS multitasking works, there appears to be quite a bit of confusion on what is actually running in the background....even from the Apple Genius Bar.
There is one iOS "tip" that I keep hearing and it is wrong. Worse, I keep hearing it from supposedly authoritative sources. I have even heard it from the lips of Apple "Geniuses" in stores.
Fraser Speirs - "Misconceptions About iOS Multitasking":