What I'm curious about is how Steve Jobs saw this coming so many years ago. He declared a post-PC world when the original iPad launched, and at the time I couldn't understand what he was saying. But for a vast number of people, a tablet now does everything they would usually do on a "computer". What's the point of getting a multi-core desktop (or laptop) when all you're going to do is surf the Net, check Facebook and send a few e-mails? For people who need a computer for more traditional tasks, those are still available and will be for a long time to come. But for a majority of people, a tablet seems to be fine.
I wonder how many people have just a tablet. No laptop, no desktop. I'd find that an interesting stat to read.
I reckon the number is (for now) still pretty small. What I'd guess is happening now, is people are upgrading their old laptop less often, and making do with a new tablet (for general browsing, social media, light email use), and an old laptop (for the tasks at which the tablet isn't great). They're not exactly "switching over" yet, but it's enough to see a serious decline in the PC market.