From the Surfin’ Safari blog:
The client-side database storage API allows web applications to store structured data locally using a medium many web developers are already familiar with – SQL.
Like cookies, you can store the databases per domain. I’m struggling to determine if the persistent storage in Firefox is the same thing. Firefox’s implementation states clearly that it isn’t available to web pages (only “trusted callers”). IE seems to be (per usual) implementing something similar, but slightly different.
Niell Kennedy wrote a good summary of the different techniques for boosting Ajax performance using local storage and why this would be beneficial.
I’m starting to get excited about HTML5. This database feature could be very useful for web applications.