Steam kicks support for Windows XP SP1
Valve seems to have begun the process of phasing out support for Windows XP starting with Service Pack 1.
From August the 31st anyone who has not upgraded their version of Windows XP with Service Pack 2 will no longer receive updates or customer support.
Of course, as long as you have an internet connection you'll be able to upgrade XP by simply accessing Windows Update feature in the Start menu.
Valve estimates that the number of users affected by this will be minimal with around one percent of Steam's 40 million users still using Windows XP SP1.