Those Atom netbooks get counted as PCs, even the early 7-inch Asus EeePC, which have very little practical use.
So, I don't mind counting the very useful iPad as a PC. You can get an optional keyboard for the iPad (if that what it takes to be labeled as a PC). The same goes for the Asus transformer.
I think that personal computing has changed in the last few years. It has become more personal (something that you can take with you without being a burden).
I also don't mind calling my smartphone a PC. I can do almost everything with it that I used to do with my desktop. Sure, there are things that you can't do with the smartphone. But the same can be said with the limitations of netbooks. And it is also true that there are things that you can do with a smartphone that you can't do with a desktop.
So for me, any of these mobile devices that allow me to surf the web, check-email, do online shopping, online banking, play games, manage my calendar, install applications, store data, be entertained (music, video), I consider them to be my "Personal Computer". It does not have to be "desktop".
Oddly, people called the CGA, 8 mhz IBM DOS desktop a PC.