Gears for Opera Mobile
You can find the technological nitty-gritty, including installation instructions in the Opera Labs article.
I’ve been using Opera Mobile with Gears to download news stories for offline usage on the ITN Mobile site, and I’m currently playing around with WordPress’ Gears powered admin interface, which enables you to blog “faster than the speed of light.” :-) They both work excellent, but as we haven’t tested this feature extensively yet, things might break on other sites. In any case, be sure to try it out, and let us know what Gears enabled sites work for you. If you find a bug, there’s of course the bug wizard.
It’s probably also worth pointing out that, besides this Gears implementation, we’re also working on support for the HTML 5 Offline Web Applications spec, which has stabilized recently. We’re not quite sure yet when that will be ready, but we’ll definitely let you know here on the ODIN blog!