I recently got an invite to the Mozilla Weave alpha, and after playing around with it for a while I can say that this product has a chance to be a very big disruptive force on the Internet.
The features provided by Weave are modest right now. It offers bookmark, history, and tab syncing, and of these features only bookmark syncing seemed to be working correctly. Other features set to be released in future versions, such as cookie, password, and, most exciting of all, extension syncing, have the potential to make Weave much more useful.
So why am I so excited about Weave, especially considering that production-quality extensions like Foxmarks already offer the same features as the current version of Weave? I'm excited because Weave has the potential to shift the balance of power away from the large Internet services and back to the user. Like many users, I gave up using browser bookmarks many years ago because I was using more than one computer on a regular basis. I started using del.icio.us, and then switched to Google Bookmarks. While I gained some useful features by using these services, I was at the same time handing my data over to a third party, relying on their good will and the strength of their security systems to keep my data private. Weave is different -- because user data is encrypted, when the data is uploaded to a Weave server, the data can still only be accessed by the user who first encrypted it. So even if Mozilla wanted to access the data (or if there were a security breach and someone stole it), user data remains safe. More importantly, even if the data were to be subpoenaed, it would remain unreadable by a third party. Of course this puts the onus of security on the client, but since Weave is open source, you don't simply have to trust the creator's word that the client-side encryption is secure.
You don't just have to be a security spook to be excited about Weave, though. I'm very interested in the possibilities for third-party applications that could be built using Weave. The hard part of building a web application is scaling it. What if you could build a web app that used Weave to store and sync all the user data instead of building out your own backend servers to do the same thing? Right now the best alternative out there to building your own backend infrastructure is to use services like Amazon S3. But again, this centralizes too much data with very few service providers. Building apps that leverage Weave would keep user data close to the user, where it belongs.
There are significant challenges that face Weave if it is to be a success. The project creators have spent much of the last year building a scalable infrastructure, and the alpha users are eagerly awaiting completion of the basic feature set that was promised when the project was first announced. The emphasis on security necessarily impacts the user experience. Not only will users have to get used to "signing in" to their browser, but they will also have to understand what is the difference between a "password" (authenticate the user with Mozilla) and a "pass phrase" (encrypt/decrypt user data). With enough testing and design iterations, Weave could be made acceptable to mainstream users, but it will take time and effort to do so.