New Tor users using Apple's Mac OSX sometimes run into difficulty opening the Tor browser bundle the first time. This could be alleviated if the Tor Foundation were to register in Apple's Gatekeeper Developer ID program. Why hasn't the Tor Foundation done so?
Caveat: I am not a member of the Tor Foundation so I can not speak officially.
The primary issue with Apple's Developer ID program is that by enrolling, the official binaries produced by the Tor Foundation for Mac OSX would be subjected to various Apple dictated stipulations and the Tor Foundation would lose autonomy over the release process.
The current verification system using open source, trusted tools by the Tor Foundation is important for the safety of all Tor users.