Big disclosure here: this is a beta in every sense of the word. Why would I say that? Well, the Google gives this warning: "This is BETA, it is not an official release, it might break your browser. Chances are it will break your browser. Please proceed with caution." Since nobody likes a broken browser, especially us "cloud people", you’ll want to be extra cautious or just wait for the bugs to be worked out.
Although Firefox is far more popular, I’m glad to see Google recognize that Safari users might want to use Google data offline too. You’ll need Safari 3.11 on Mac OS X 10.4.11 or 10.5.3 to kick these tires and take your mail, docs or RSS feeds with you when disconnected. For me, Gears is a must: it’s part of my cloud backup plan.
(via Google Operating System)