I think computer systems are the ones that are the most impacted by daylight saving time changes. The amount of effort that is necessary to make sure a change

I think computer systems are the ones that are the most impacted by daylight saving time changes. The amount of effort that is necessary to make sure a change goes smoothly might be higher than you're thinking. I worked at a medium-sized billing business in 2007 during the switchover from the beginning of April to what it is now. Our team spent a great deal of time going through every single system, making sure that they had new DST tables. If I remember correctly, we still got bit because the MySQL service on a server hadn't been restarted since we upgraded the rules. We also had problems because of a java service since java ships its own copy of the time zone database. For historical reasons, the dates and times on the mainframe weren't stored as UTC. We would do billing during the night in batch jobs. After suffering through problems a few years, we finally figured it was easiest to simply suspend the batch jobs during the whole "repeated hour" in the fall, so that we wouldn't get out-of-order timestamps in various places.