Just to follow up on this thread, I started looking at Google Gears today and this immediately caught my attention as being a source of potential problems for my application. If a user regularly accesses my application from Internet Explorer, but one day installs Firefox and makes it their default browser, my application has effectively lost their local data. My opinion is that, being a feature of the application (rather than a feature of the browser), the local database should be entirely independent of the client browser.

I've raised issue 123 [1] in the hope of getting this problem addressed, one way or another.

[1] http://code.google.com/p/google-gears/issues/detail?id=123