Windows XP was released on October 25, 2001, and it became the most popular operating system everywhere around the world. There was hardly any computer that didn't have Windows XP installed. It has been around for a long time and had many updates, the last "Service Pack" update being the third, released on April 21, 2008. After Windows Vista came out, people were still hooked on Windows XP and you could still see more XPs installed on computers than Windows Vista, as it had it's issues. Even after Windows 7 came out, which was a success and is the most used Windows as by now, Windows XP has still been the second most used operating system, especially in Asian territories. You can see the chart below, of 2013's 7 most used operating systems below:
As you can see in the chart, despite even Windows 8.1 being out now, Windows XP is still the second most operating system in the world.
Microsoft announced it sometime ago that Microsoft will end all support for Windows XP in April 8, 2014. As of now, only a few months are left until the end of Windows XP's support. End of support means that there wont be any new updates, no security updates, no official downloads, and although you will be able to still use the Windows, but it will be completely outdated. Outdated means that softwares and video games wont support it anymore, as it will require a newer version of Windows such as Windows Vista, Windows 7 and Windows 8/8.1.
So, if you are still using Windows XP, now's the right time to upgrade your Windows!