Who owns the data? And what if the service is shut down because they think you violate the TOS?
For the IPad, I agree they aren't PC replacements, but even for this:
"but mainly ones PCs aren't very good at – anything involving touch, of course, plus viewing videos or books"
Since when were netbooks and laptops not good at this? I do both just fine on mine. And I'd say they're better suited, as you can just place it on your lap with the screen angled just right, where as the IPad has to be held in your hands.
"not just netbooks, whose popularity as the leading companion device has already been eclipsed by the tablet."
Tablets now sell more than netbooks? Since when?
"However, according to DisplaySearch analysts, if the iPad is categorised as a mobile PC rather than an oversized iPhone, Apple is now the largest mobile PC vendor in the US,"
Worldwide, they're smaller than HP and ACER ( http://www.reghardware.com/2010/12/07/displaysearch_q3_2010_mobile_pc_sales/ ). And as that article points out, it ignores smartphones; Nokia sell way more than Apple. It's a rather contrived statistic to handpick a category that counts the IPad as a "mobile PC", but not other handheld mobile computing devices.
Talking of Nokia, it's odd to have an article covering all the alternatives, but to ignore the number one smartphone company.