There are a lot of people who can't use the shortcut functions from the settings app to replace abbreviation like "omg" with "oh my god" etc. because of a iCloud bug. (I'm one of the victims -.-)
Double@ is cool, but there is a even better solution, but you have to make your fingers dirty
Tweaks like Double@ doesn't work in security fields, in apps like iFile and Cydia and they can't be used if you are in Safe Mode etc.
There is an always solution which doesn't even need a tweak, mobile substrate and works everywhere and anytime. You just have to place words, email adresses or passwords (for example for the app store) in your keyboard. If you hit your modded key and hold it, you'll see a box with your data, which you can select. I'm doing this since iOS4 and it works great. iOS6 is a little difficult, because they completely changed the keyboard structure, but it's still possible. I'm using it on iOS6.1 and it just awesome.
You should use keys like ?, $ or &, which are always on the keyboard. Here you can see just one example. You can also set emojis
After hitting the button and sliding to the desired, the predefined text will apear magically
View attachment 26773
I can explain it if someone is interested