You would be amazed at the amount of people who do not know how to close apps after they have finished with them. Especially bad if you travel across the globe and your phone is on 3G in each country. I saved one of my customers hundreds of pounds for data roaming which he thanked me greatly for.
Absolutely, I've had every incarnation of the iPhone so thought I knew my way around them pretty well. However, I only just learnt how to close the apps properly due to a post on here earlier! That is probably the cause of my horrendous battery drain.
