Gメールがオフラインでも使える

オフィシャルGメールブログより
New in Labs: Offline Gmail

Today we're starting to roll out an experimental feature in Gmail Labs that should help fill in those gaps: offline Gmail. So even if you're offline, you can open your web browser, go to gmail.com, and get to your mail just like you're used to.

We're making offline Gmail available to everyone who uses Gmail in US or UK English over the next couple of days, so if you don't see it under the Labs tab yet, it should be there soon. Once you see it, just follow these steps to get started:

1. Click Settings and click the Labs tab.
2. Select Enable next to Offline Gmail.
3. Click Save Changes.
4. After your browser reloads, you'll see a new "Offline0.1" link in the upper righthand corner of your account, next to your username. Click this link to start the offline set up process and download Gears if you don't already have it.

とのことなので、日本ではまだ使えないのかな？

今見た限り、まだのようです。