Gmail offline is finally here! As per my message on twitter; It's fast – even better than Gmail online. Faster than desktop apps. The internet revolution is here!
You'll need to enable Gmail "Experimental features" first. I've forgotten how to do this, but I think it's in the admin "cpanel" for Google Apps for Your Domain. I'm not sure about Google-proper Gmail.
Once you have that;

1. go to Settings (in Gmail)
2. then Labs

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