This is a free tool that can remove and disable the 'Get Windows 10' notification area icon on Windows 7 and Windows 8. Newer versions can also disable 'Upgrade to Windows 10' behavior in the Windows Update control panel.
For those of you that are still dual-booting (I have a box in that situation) and watching the steady march of Windows 10 on to existing Windows (X). This stops that process (including deleting the Windows 10 storage folder. I have heard that Microsoft is developing a work around to re-start the Windows 10 upgrade. But in the mean time - a great form of non-cooperation with the Matrix