Service Pack 1 for Windows 7 came out on general release way back in 2011, but up until now it has been an optional update. That changes from today, with SP1 auto-installing on any Windows 7 machine set to install updates automatically.
Microsoft's blog post highlighting the change notes that this won't affect corporate systems: "This update only applies to Windows 7 consumer PCs that are not managed by a Microsoft management tool such as Systems Center Configuration Manager (SCCM) or WSUS Server. SCCM and WSUS administrators still have full control over the release of Service Pack 1." Nonetheless, rolling out the update makes sense if you haven't already: from April 9, only Windows 7 SP1 will be supported.
Windows 7 SP1 to start rolling out on Windows Update [Blogging Windows]