It may seem extreme, but users who can't resist checking Facebook and Twitter in the middle of the night are not alone. According to the March 2010 "Gadgetology Report" from consumer electronics site Retrevo, 48% of social media users log in to the sites either during the night or as soon as they wake up.

Users under 25 were more likely to check or update their social network status after bedtime, with nearly one-fifth saying they did so anytime they woke up during the night.

Almost as many younger users (18%) checked the sites in the morning before getting out of bed, while 17% of respondents of all ages turned to Facebook and Twitter before TV in the morning. iPhone users were notably more likely than average to do each of these activities, with 23% saying it was how they got their morning news compared with 16% of all social media users.

Source: eMarketer
http://www.emarketer.com/Article.aspx?R=1007580