David Chartier on Lion:

Just like switching between apps on an iPad or iPhone, or even restarting the device, Resume is Lion’s official support for third-party Mac apps to pick up right where they left off, even after a restart. That’s not merely a good idea in iOS, it’s just a good idea for any reasonably complex computing device—especially one that is designed to multitask and juggle many apps and open windows with ease.

That really is a killer feature — can’t wait to see Windows try and implement that one.