One of the big sticking points with using web applications is that you have to be online to use them. No internet connection = no access to the application. It looks like Google is working to plug that hole with the beta release of Google Gears. Google Gears is a browser plugin (still in early beta release) that allows you to use web applications even when you are offline.
While initial reaction has been that the plugin is a good proof of concept, Gears still has a ways to go before being unleashed onto the world.
One of the stumbling blocks right now is that Gears only provides the read functionality of the read/write web. There is still a lot of work that needs to be done before Gears will provide full read/write functionality. Plus, there is only one app in Google’s stable that works with Google Gears and that’s Google Reader, although there has been strong hints that Gmail and Calendar will be next. So, rather than this being a beta release, I consider this more of a proof of concept release.
Regardless, the release of Google Gears is poised to solve one of the major hurdles towards mass acceptance of web applications as a replacement for their desktop counterparts. For that reason Google Gears is an important release in the evolutionary cycle of web application development.
For more on how Gears works technically, there is a good post by Nick Gonzalez at TechCrunch.