Multitasking makes it easier to flip back and forth between 2 apps easily, when you double click the home button to enter the new thumbnailed multitask screen, it always highlights the previously opened application (or the 2nd in the list, as it were) so if you are for example copying multiple items of text from one app to another, you can use the following flow to quickly and repeatedly switch between 2 apps:
Double Click home, hit the center of the screen; this will always return you to the previous app.
Once you have switched apps in this manner, the order that they appear in changes (basically switching the 1st and 2nd positions around). Repeating the Double Click home and center tap will flip you back to the first app