According to the development ticket for the Google Gears patch:

The patch adds all static files used in the admin interface to a single offline storage. That speeds up page loading a lot, as it serves virtually all requests for static files from the computer’s HD instead of the network. So instead of 50-60 requests to the server on some pages, there are only 2-3.

Personally, I’m waiting for the WordPress 2.6 demo to be updated with a supporting alpha version so I can try Google Gears out. I just certainly hope it turns out to be more reliable than some other Google Gears implementations have been.