Apple has pushed back the deadline on its polarizing sandbox rules until March 1st, giving app developers more time to toe the line on the new guidelines. Instituted as part of Mac OS X Lion, the new rules apply on all apps offered through the Mac App Store and put significantly tighter controls on the permissions allowed to programs. The idea behind sandboxing is that apps that have been compromised by malware no longer have access to the entire system, as each program is afforded only a finite amount of access due to a new permission system. The controls that Apple's put in place curtail some key functionality for certain apps, such as limiting them to a single, isolated file system except with user approval to look elsewhere.
Unfortunately, the popular FTP app Transmit won't be allowed to directly display or interact with disk contents, and system-wide keyboard shortcuts like those used by TextExpander might not work. These changes probably won't have a significant effect on the majority of applications in the Mac App Store, but for those that do, their developers are faced with either cutting functionality or taking their software off the App Store and potentially losing a huge chunk of their user base. So while it might make Mac OS X safer from the threat of malware, power-users accustomed to extremely powerful apps may be out of luck.