Google gears includes SQLite. Awesome.
At work, we have a whole bunch of tablet PCs. I've always been a little bit hesitant about the worth of them for our valuers.
We've relied on a 3rd party solution for data capture, so our valuers can draw up floor plans and capture information about the property they are at.
To get the information back is a mix of air card (for wireless connectivity), soap services, a .NET client application, a .NET server built by someone different to the client software provider, a custom XML format which has parts resembling CSV in XML, and bits of our own PHP which were hastily patched together at the last minute, then promptly shelved to do more important things.
You can perhaps see where I'm a little bit hesitant about introducing features to our tablet users. However, you can get a few different Firefox extensions to improve tablet PC usage (scrolling for instance, or enabling keyboard input on the address bar), there's the CANVAS element, SVG support, and now Google Gears providing offline support, as well as a full blown database backend and the ability to offload intensive computing processes elsewhere.
It's no longer inconceivable for us to provide the floor plan capture software over the web, or provide maps to locations for offline usage through Google maps...