Ok so the deal is this. 99% of instability is caused by bad and faulty hardware such as bad ram..etc. I've also had flaky unstable OSX machines at work. I could easily say its crap and make a blanket statement but I ran a memtest on it and it was bad ram - on two of the 10 dual 2.5Ghz G5's. If I didnt take the time to figure out the issue, then we could have just chalked it up to sh*t computer or crappy OS which was not the case.
Microsoft caters to all kinds of hardware, its up to the vendor, being Apple, Dell, HP, Gateway or even yourself if you're building your own, to decide what hardware is reliable, what hardware has good driver support etc. If you buy crappy hardware with poor support, then you will end up with a crappy experience.
I think that much of the ill will stems from the fact that people should not be forced to buy new equipment just so that they have a printer or scanner that works with their OS. For instance, if your average consumer is upgrading their PC, the new one will probably come with Vista. There's a chance that they are going to experience difficulty when they are setting the thing up when the printer drivers don't allow them to print. People then tend to blame one of two (or both) things: Microsoft (very likely), or the manufacturer of the malfunctioning printer.