There are a few new features in Lion that you might not have heard about or used yet: Versions, Autosave and Resume. Versions aims to bring the functionality of Time Machine to your documents. This means that you can view several versions of your documents with the changes that happen over time even if you have deleted or added new things to the document.
Autosave is a feature that makes certain apps save your documents automatically after a certain period of time, to avoid losing important changes that you may have made after your previous save. Additionally, Resume, is a feature that allows you to open apps and find them to be in the state that they were in before you closed them. Want to learn more about them?