How does the midnight sun affect the people who live in the Arctic or Antarctic?

They have to deal with all-day sunlight the same way that people who work the night shift deal with trying to sleep during the day - they usually need to darken their sleeping quarters to help them sleep. In generally though it tends to encourage them to stay awake longer and sleep less and still feel like they are getting enough sleep.

The midnight sun poses special challenges to religious people such as Jewish people who have religious rites based around the 24 hour day/night cycle. In the Jewish community this has given rise to a body of Jewish law in the polar regions, which attempts to deal with the special challenges of adhering to the Mitzvah in such conditions. Another related religion that suffers from this is Islam, where fasting during daylight hours in Ramadan would imply total abstinence.