Why hasn't Vista sold well?
When we tell them that the new OS is faster and better, only to have the upgrade break a piece of software that we don’t care about but they really do, we burn our likelihood that they’ll ever willingly upgrade again. Every time we tell them that they can now easily edit video or make DVDs, only to have them abandon their first effort in frustration and never attempt it again because our software sucks, we drive them closer to indifference or resentment toward future technology.
So when our nontechnical aunts refuse to upgrade from their Pentium III PCs with Windows 98 that work well enough for them and are set up exactly how they prefer, we have nobody to blame but ourselves.
The upgrade market for average PC owners is dead. We killed it.
It's not just "average" users – I consider myself to be above average (I used to fix computers for a living) and my auxiliary (i.e. non-Mac) laptop still runs Windows XP. The vast majority of software I care about still supports it, so why switch?
There's another reason for Vista's non-adoption rate that Arment doesn't mention – the ridiculously high number of different versions of the product. There are four different editions of the product (Home Basic, Home Premium, Business, and Ultimate), ranging in price from $200 - $320. Asking the "average" user to make that decision is practically planning to fail. Don't even get me started on Service Packs.
Read Marco.org - Why hasn't Vista sold well?.
(Via Daring Fireball.)