Draft folder!

This is a really cool tip I just discovered recently. At first, when you look at the Mail interface on your iPhone, you don't see any way of saving an email as draft. It is however possible! You simply have to press the "Cancel" button. A dialog will pop up and ask you if you want to save the message or not. When you choose to save it, Mail will add a "Draft" folder in this specific account and you'll be able to continue your message there!