When an app is loading on iPad or iPhone you can pause the loading process by touching the app with your finger.
I can see this being useful if you're on 3G when you start installing a large app and you don't want to chew through all your 3G bandwidth, you can then pause the loading process until you can connect to a WiFi network.
[crarko adds: I tested this, and it works as described. I have an iPhone 3G and have used this before.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20110105134142554