My worry about this is that it is yet another place for the implementation quality of your browser to be largely responsible for the security of your data. Whil

My worry about this is that it is yet another place for the implementation quality of your browser to be largely responsible for the security of your data. While I think Microsoft does a fine job of security R&D, the tend to massively fail when it comes time to actually deliver. At a fundamental level, simplicity of mechanism has to be part of any secure system. Every major MS stack (Windows kernel+core API, IE+ActiveX+JScript, Office+VBA) is just too huge, and has too many little back doors around the security infrastructure built in for performance and backwards-compatibility. Now, if they truly willing to commit to using a substrate like Singularity for their trusted computing base, we can talk about security. The better way to handle this, of course, is separate browser runtimes for separate applications, ala Prism/XULRunner. Each desktop app should have a whitelist of hosts it's allowed to access, and sharing can be accomplished via normal local system channels.