Obvious Apple App Store Thing

I guarantee the App Store would see a significant boost in downloads if they'd just build in a "recommend this app to a friend" option in the iPhone. You could put a little person icon on the lower right of an app when it's wiggling during the change-icon-placement mode, then that brings up a popup or an ABPicker that lets you send an SMS message to someone in your contacts; the message will contain a link that pops up the App Store page for that app when the receiver clicks on it.

The number one problem with the App Store is finding good apps. Word of mouth is still the best way to hear about good ones, so why not enable that functionality on the phone itself??