Online / offline RSS browsing has been a horrible compromise for a long time. The tools were lousy, synchronization didn't work well, or they made stupid compromises like only downloading headers.
That's why Google Gears and Google Reader are so interesting. Gears is a DLL that you can install in your browser that creates a persistent store for using web applications offline, and synchronizes that store with data on the 'net when the application comes back online. Google Reader has implemented it with a simple button that says "Go Offline". Press the button, and Gears does a quick synch with up to 2000 unread posts, and away you go. Press it again later, when you're back online, and Gears will synch up with the Google Reader database marking the stories you read offline as "read".
Simple, and very effective.
Some pundits are pointing to this as yet another example of Google's assault on Microsoft's turf. The argument is that you can now turn the Google office apps into online and offline apps and have the best of both worlds. Not so fast, say I. Google's spreadsheets and word processors are a far cry from the sophistication of Office 2007. It's going to take a lot more than simply making them useful on an airplane for Google to unseat Microsoft.
But for reading RSS feeds it looks like just what I've been looking for.