Wil Shipley: Real Security in Mac OS X Requires Apple-Signed Certificates.

"The problem Mac developers are facing is that the two that Apple is enforcing on the Mac App Store (Sandboxing and Code Auditing) are implemented currently to be actively bad for developers and not particularly good for users. And the method that would provide the most benefit for developers and users (Certification) isn’t enforced broadly enough to be useful."

As a developer, I'm not too thrilled about required sandboxing in the Mac App Store for existing apps. New apps sure, but… it's all very Darth Vader-ish: