Google announced on the official Gmail blog a handy new upgrade to the Offline Gmail labs app. Before the update, you could enable Offline Gmail and it would use specialized heuristics to download messages for offline use.

With the new update, once you enable Offline Gmail, you can find some customizable options under the “Offline” tab in Settings. You can now select specifically which labels to download and how deep into your mailbox you would like the downloading to begin. Once the settings are saved, the app will immediately start downloading any emails weren't already synced to your computer.  Of course, less downloads means faster Offline Gmail so you should be careful with the settings.

It's a substantial upgrade to a very handy lab application for commuters or travelers.