WordPress.com is the latest Web service to get Google Gears support. Now users who log in to their dashboard will notice a new button in the top right-hand corner called "turbo." Clicking it will make use of Google's Gears (which is currently Firefox and IE-only), offloading some of the data from the cloud into your browser cache. In this case, it's the latest 200 files from your WordPress media library, the same files you access to stick into blog posts.
A post on the official WordPress blog by creator Matt Mullenweg notes that the feature has been in development for more than a year and that bloggers are going to notice it the most when on a bad Internet connection. In practice, it should speed up writing a new post and make it faster to drop in photos you've already uploaded to the service's cloud storage.
One thing Gears is not being used for in this case is offline access, or a way to let you use the blog authoring tools while away from an Internet connection. Other tools that have taken advantage of Gears include Google Docs, Reader, Remember the Milk, and some Zoho apps. With Gears' recent movements toward providing more than just a cache, we're also seeing services like MySpace use it to speed up its inter-network messaging.
Update: I'm told this feature will be making its way into the next version of WordPress.org, also known as the hosted version of WordPress. You can read about some other things coming to that version (v2.6) here.