Working offline with Gmail just became a little simpler. You have had the option to download your messages, but it was fairly scatter shot. With this new feature you can specify what you want to download for use while you will not be able to get online. While email generally does not take up much memory, it can under some circumstances. Now you do not have to worry about downloading everything to make sure you have those few emails.
"From now on, once you enable Offline Gmail from the Labs tab under Settings, you can choose which messages get downloaded. On the Offline tab under Settings, you'll see your current settings and be able to set how much mail you want to download from each of your labels. I chose to download everything in my Inbox and important labels, as well as recent messages from the last month from other labels."