When Asus introduced its Eee netbooks running Linux, it heralded a flood of cheap-and-cheerful small machines that used tiny amounts of cheap USB-connected flash storage and didn't run Windows.
Users flocked to them because they were cheap and in many cases mistook them for small laptops that would work like their familiar full-size laptops.
PC makers switched to putting Windows XP on their netbooks. That still didn't make a netbook a real cheap notebook, though — for that you needed an expensive ultraportable with a business price tag — but it validated the concept.
As did the way Microsoft reacted. Microsoft saw netbooks as a significant enough threat to explicitly develop Windows 7 to run on them.
That was also a response to the problems of Vista, which only ran well on a brand new PC with a powerful new processor and the then-rare full 4Gb of memory. Having then-Windows chief Seven Sinofsky show off the netbook he was using as his main PC on stage at the Windows 7 PDC showed that Microsoft was serious about not letting Windows 7 be another 'bloated' operating system (on a new PC Vista actually performed rather well).
And knowing your boss is running daily builds on a netbook has to concentrate the mind of a Windows developer on performance and battery issues. Every PC user saw the performance benefit of that work.
But by taking netbooks so seriously, Microsoft also enabled the race to the bottom that has culminated in $99 Android tablets. Instead of user experience or usability, OEMs concentrated on knocking out the cheapest possible devices they could sell. Never mind the quality, feel the width - or never mind the profit, we'll make it up in volume, as the old jokes go.
Perhaps, if Microsoft hadn't blinked, if it had said that Windows didn't actually scale down to a tiny little screen and a hard-to-use keyboard, if it had concentrated on making Windows a powerful premium experience that was also easy to use, the PC market wouldn't have collapsed quite the way it has.
This, admittedly, would have relied on OEMs actually delivering premium hardware that wasn't compromised by crapware - or on Microsoft launching its own PCs much earlier than it did.
Microsoft would have had to come up with something for the budget market and it would have had to be something that ran Office - but given that Microsoft discontinued the free Office Starter offering, it's likely that netbooks running it didn't actually convinced many people to upgrade to pay-for Office.
Perhaps ignoring netbooks instead of legitimising them as a major PC sector would have kept PCs as the high-margin devices like Apple Macs.
Tablets would still have come along, but the PC industry wouldn't have cut its own throat and devalued the PC name in a race to the bottom. And maybe that would have left space to deliver more Windows 7 ultraportables that could do what people actually wanted netbooks for, while Windows RT was under development.