Most users who uses genuine Windows 7 products will be getting SP1 over Windows Update, Microsoft stated.
"Windows 7, Service Pack 1 will help keep your computers well supported by delivering ongoing updates, many of which have been made previously available through Windows Update,"

Microsoft made available the Windows 7 and Windows Server 2008 R2 SP1 to its Microsoft Developer Network and TechNet subscribers, on February 16. and has been available in three different one for 32-bit and two for 64-bit Windows 'x64' and 'Itanium'.
Today 22nd of February, Microsoft finally open and offer SP1 to the public for free download and also deliver significant updates and bug fixing via Windows Update feature.
According to Microsoft Win 7 SP1 page, the updates packs with new enhancements to in Windows 7, such as improved advanced security when connecting you PCs to HDMI audio devices, printing over the XPS Viewer, and other various features.