NEWS: On July 13, 2010, Microsoft is officially ending its support for Windows XP SP2, windows 2000 server, and windows 2000 client. This means, that the company will no longer be providing hotfixes, security updates or add-ons for this OS applications.
IMPACT: This definitely means something valuable for big companies using 25+ computers. They won't be getting any security or support for their industry compliance win case of any issues. For them, better option is to upgrade to Windows Vista or Windows 7.
But for small 2 room companies, or individual professionals, or also household users, this is not a big thing to worry. Because the current security levels should be enough for their work continuity. Also, all the till-date updates and fixes will also remain available to public for their use in future as well.
HISTORY: Microsoft has done similar thing in past, when support to XP SP1 was stopped on Oct 10, 2006. No more new updates, but still the older ones are available on their download site.
FUTURE: Its again in news, that Microsoft will end its support for XP SP3 as well on April 8, 2014. It means, complete XP will be a past phase in Microsoft's business lines.
REASON: The reason for this shift from XP to later versions (Vista and WIN 7), as suggested by Mr Scheiber from 'workstart.com', will allow company to focus on upcoming technologies, and increasing challenges in their upkeep and maintenance.