It’s a bare-bones, three-part architecture in Google Gears. Blogger Dare Obsanjo looked behind the curtain and found Gears wanting with respect to data synchronization:

What happens if I’m on my laptop and I go offline in Google Reader and mark a bunch of stuff as read then unsubscribe from a few feeds I no longer find interesting.

The next day when I get to work, I go online on my desktop, read some new items and subscribe to some new feeds. Later that day, I go online with my laptop. Now the state on my laptop is inconsistent from that on the Web server. How do we reconcile these differences?

A data sync would reconcile those, and Google’s developers provided some suggestions on accomplishing it. Obsanjo found Google’s approach lacking for web application developers who aren’t Googlers already:

It seems that without providing data synchronization out of the box, Google Gears leaves the most difficult and cumbersome aspect of building a disconnected Web app up to application developers.

“Google has tossed a database API at us and called online/offline synchronization solved,” James Robertson said in agreeing with Obsanjo’s point.

It’s probably instructive that online/offline data syncing tends to be the sort of service that requires payment for commercial software that can do it. Perhaps that’s a market for a clever developer: build a Google Gears sync and charge a nominal fee for it.