Google slowly continues to grow in the way it uses Google Gears. Now, Gmail goes offline! Using Gears technology, Gmail begins the building the bridge between web app and email client. After activating the offline mode in Labs, clicking the new offline icon next to one's email address at the top begins the process of bringing all your Gmail -- every gig of it -- to your hard drive, keeping it synchronized with Google's servers.
The offline experience adds an outbox and faster response times, although the initial synchronization can take a while depending on the amount of mail in your account. Thereafter, everything is kept sync'd. Offline mode kicks in automatically when the connection to Google is lost and everything is updated when the connection is restored.
Warning! Being a Labs feature, it's technically experimental in nature and you might hit a few snags here and there. It also may take a few days before you see the offline feature in your Labs offerings.