Daylight Saving Time (DST) or Summer Time (as they call it in Britania) was usually something we used to set by hand in WordPress releases beyond the in-development version 2.8. This was not really painful, but being a great software, WordPress guys described it as a “Lame”.
What is daylight saving time?
Daylight saving time (Summer Time) is the convention of advancing clocks so that afternoons have more daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in autumn. Modern DST was first proposed in 1895 by George Vernon Hudson, a New Zealand entomologist. Many countries have used it since then; details vary by location and change occasionally.
In WordPress 2.8, they added Timezone enhancements for PHP 5 so you can choose a city in the same timezone as you for Timezone in Administration > Settings > General.
Old WP time settings
New WP DST settings