Timezone surprise for U.S. systems
Thanks to the Energy Policy Act of 2005, United States computers must account for the altered daylight savings time shifts. Systems that use UTC (and the misnamed gmtime(3) system call) instead of a local timezone that wanders will not be affected. On Unix, the fix should be as simple as deploying an updated timezone file.
If possible, always run Unix systems in UTC, though converting existing systems or ensuring UTC is used properly by all applications may be time consuming and expensive to implement. On known conversion problem: a system runs in UTC, and starts an application in UTC. A user with a custom timezone set restarts the application via sudo, causing the application to run under their custom timezone. Hilarity ensues.
Tweaking sunrise and sunset to save energy, while providing kickbacks to the oil industry, all while vehicles still guzzle down insane amounts of fuel: your friendly local government hard at work.
On a somewhat related note, TLS (the protocol formerly known as SSL) stops working in 2038 due to the use of a 32-bit Unix time value. But that’s years away. No need to worry!