So, I was looking at Google Reader and noticed a link in the upper right - Offline (new)..
What's that? Turns out, Google has a project called "Gears" that provides Javascript hooks that will interface with a few locally running services: Cache, DB, and asynchronous thread pool.
This is great, cross platform too. It's SmartClient (and no, MSFT didn't invent the term as far as I know) in essence that it also provides offline capability. You'll still need to deal with updates, etc.
Google Gears: Enabling Offline Web Applications
Google Gears is an open source browser extension that lets developers create web applications that can run offline.
Google Gears API Developer's Guide - Home
There are a few cool things coming out in the Visual Studio 2008 Orca's release - most notably SQL Compact Edition and Sync Services. This framework provides the offline synchronization ability for your offline clients.
Steve Lasker has been doing quite a few webcasts, posts, presentations on the subject. Definitely check it out if you're in the Thick Client mode. In fact, check it out if you just need to keep different persistence stores synchronized. There's lot's there and useful outside of Smart Clients as well. If you think about what we spend quite a bit of time when we're building applications, a good chunk is keeping multiple databases synchronized.
Steve Lasker's Web Blog
Sync Services forADO.NET and SQL Server Compact Presentation