I realize this information was published with the feature list for the iOS 5 update, but it's somewhat buried so this might help some people:
The shortcut feature can be found by going to Settings > General > Keyboard > Shortcuts (listed at the bottom)
I actually find this is a very handy feature, especially if you have to send a quick response while driving (and you don't have an iPhone 4S/Siri).
It seems that the shortcuts work through autocorrect. So when you type your predefined shortcut keys, the autocorrect bubble will pop up with your message. You'd simply hit the space bar or the Send button to send the message.
The shortcut feature can be found by going to Settings > General > Keyboard > Shortcuts (listed at the bottom)
I actually find this is a very handy feature, especially if you have to send a quick response while driving (and you don't have an iPhone 4S/Siri).
It seems that the shortcuts work through autocorrect. So when you type your predefined shortcut keys, the autocorrect bubble will pop up with your message. You'd simply hit the space bar or the Send button to send the message.