The choice of four CPU architectures between Windows RT and Windows 8 devices and the resulting tradeoffs will confuse users and slow tablet and laptop uptake.

Tablet and touch buyers will like the Windows 8 UX ("Metro") but many conventional PC buyers will be put off by it.

It will take a year for ISVs to fully stock the Windows Store with a range of apps.

Microsoft will struggle to communicate the richness and complexity of Windows 8, and that messaging will have to go through several iterations while Microsoft, OEMs and retailers work through how to create a message that works.

Such challenges will lead to slower than usual Windows upgrade cycles, writes Gillett.