Attention Windows 7 users: If you haven't yet installed service pack 1 (SP1) for Windows 7, you should do so as soon as you can. Without SP1 installed, Microsoft's support for your operating system ends Tuesday, April 9th, 2013.
This isn't unexpected or otherwise shocking news. Microsoft has always supported the previous (or in this case, lack of) service pack for 24 months after the current service pack was released. Windows 7 SP1 was released back in February, 2011.
"Support ending" for Windows 7 (no service pack) means that those important security related updates released on Patch Tuesday won't be made available for your version of Windows. The solution to this problem is really easy: update Windows 7 to SP1.
You can read more about this directly from Microsoft, including more about the Windows product lifecycle in general: