For all you speed demons out there, iOS4's multitasking is a little bit cumbersome. Sure you can work in one app, load up the switcher, and then select the app you would like to switch to, but in most cases, there's only a couple of apps you need to use simultaneously.
If you find yourself switching back and forth between two apps quickly, i.e., App Store and Safari, then LastApp is a true gem. This time-saver has been around for a while, but it hasn't received much attention...