WordPress.com just recently went live with Gears support for accelerating the user-interface, and the upcoming WordPress 2.6 release will also bundle Gears.
Andrew Ozz, a member of the WordPress team and the person responsible for the Gears integration wrote the following guest post on his experience working with Gears:
I thoroughly enjoyed working with Gears. After checking the excellent API documentation and examples, the test implementation of a ManagedResourceStore in WordPress was ready to go in about an hour.
After that I only had to refine the various status messages and user prompts and the first step of implementing Gears support in WordPress was ready for public testing. That was the fastest and easiest integration with another open source software I've had the opportunity to contribute to.
Currently WordPress implements Gears support in a somewhat "non-traditional" way. It uses only the local storage to cache all static files from the admin interface on the user's computer, eliminating needless requests to the server and improving page load speed, quite significantly in some cases.
Some of the limitations of this are that Gears prompts for permission on each sub-domain, so when a user has several blogs on WordPress.com, it will have to be enabled for each separately. Another is that although all files are served from the local storage in SSL mode, the browser reports that the web page is partially encrypted.
The Gears support is already live on WordPress.com, and is included in the next version of the self-hosted WordPress, that is due in a few days.
In my opinion Gears is more than an easy way to enable online applications to work offline. It extends the web browser into an OS independent application development platform. I won't be surprised to see some very different web enabled desktop applications built with it.