Stick to odd-numbered releases, they're like LTS.
Tablets and keyboards are the new laptops.
Desktops will increasingly have to prove their value in the market. In a world of booming connectivity and mobility, desktops (and even laptops) are legacy technology. All hail gestures and keyboard shortcuts.
Windows Vista is Windows NT version 6.0; Windows 7 is actually version 6.1. Similarly Windows XP was version 5.1; its predecessor, Windows 2000, was 5.0.
Windows Me was version 4.9 of the Windows 9x code base (whose first version -- as an obvious successor to Windows 3.x -- was 4.0, Windows 95).
The funny thing is that during all those transitions, the basic Win32 API stayed more or less stable. The programs I wrote for XP (or even Windows 2000) still work well in Windows 7. They just don't have the visual bling (which my customers don't need anyway).