Microsoft Announcement: Windows 10 will be released as a free update on 29 July
This will be Microsoft's last major release of Windows before they move to the new “Windows as a service” system (i.e. automatically rolling out updates when ready)
Windows 10 will be offered as a free upgrade for users of Windows 7 and Windows 8.1 within the first year. So if you qualify there is no rush - you have until July 2016.
An interesting observation is that when Microsoft upgraded Windows 8 to 8.1, they restored a version of the Start menu. It looks like Windows 10 will bring back more familiar features from Windows 7 and combine them with the modern look of Windows 8.1.
Other changes will see Internet Explorer being replaced with the browser called 'Edge'
Setting the 29 of July as a date for release could help accelerate the development cycle, however as with most Microsoft releases we would recommend you wait a few months until the inevitable bugs are ironed out.