The original version of this article incorrectly conveyed the restrictiveness of the default security in this OS X update, and has been edited to reflect the scope of software affected. Joystiq apologizes for the error.]
Apple OS X 10.8 Mountain Lion, which just started its "Developer Preview" period and will be released to the populous sometime this year, features a security protocol called Gatekeeper, which prevents unsigned applications from running, depending on user preferences. Gamasutra
reports Gatekeeper is set to only allow applications from the Mac App Store and from developer who've registered with Apple.
This means that, for any games and apps made by designers who have not registered with Apple, you will have to adjust Gatekeeper's initial restrictions.
Since you can allow content from unidentified/non-App Store sources, it doesn't seem like the system itself is inherently malicious or anti-gaming. It is, however, prohibitive, and may affect off-store apps downloaded by users unfamiliar with Gatekeeper.