I think the thing with Vista was that it was possible to have a PC that was running Windows XP very well, but under Vista it was a total dog. Of course, flash ahead a few years now and if you have a PC currently running Vista well, it's likely going to run Windows 7 even better. This significant downturn in performance is what turned a lot of people off.
Secondly, driver support wasn't good at the launch of Vista or with any of the betas. However, that same thing really hasn't been true with Windows 7. So, obviously having a bad driver experience with Vista would certainly turn you against the OS pretty fast.
Next, in the original release (prior to SP1), the UAC feature was way over the top in turns of being completely aggravating. And since XP didn't have this feature at all, that really drove some people mad. Now, with Windows 7, (and Vista SP1), they really tuned down the annoying part of UAC while maintaining the functionality part.
Finally, there were quite a few annoying things with Vista (like slow file copies, slow network file copy performance, and various sys admin tools) which just flat out didn't work correctly. So, this got the IT community going off on the release which somewhat turned into a word-of-mouth campaign against the OS.
So, I'll be honest, I've been a certified MS guy for a long time. Vista was the first OS that MS released (aside from ME) that I didn't put onto any of my machines at home. I simply wasn't that excited about it and saw no real incentive over Windows XP to plunk down my money. I use Vista at work (it's on my laptop) and my wife has a laptop at home with Vista now....and it's just fine. But I did pony up the $$'s to buy a copy of Windows 7 (well, I got Vista with a free voucher for Win7)...but I have not loaded Vista onto my machine...I've just used Win 7 RC1. So, I've not sung the praises of Vista...however I have been very impressed with Win7, I've told people about it and I'm genuinely excited for a new MS OS.
As far as "sticking it to Apple". I'm not sure that Windows 7 is really going to have a big impact. The people who buy and use Apple, buy quite a alot into the "trendiness" of it...and the release of Win7 is not going to make PC's appear any more trendy. Also, people who use OSX mainly praise it for it's lack of a centralized registry, viruses, spyware, malware and such. And unfortunately these things aren't going to vanish with Windows 7 either. So, I highly doubt there will be much in terms of a install base % change coming anytime soon. If anything hurt Apple recently, it's the downturn in the economy.
Honestly though, I'm not sure if driver support was the only thing. It ran slowly on lesser hardware. I mean, I have a very optimized SP2 vista clean install, and seven(mostly unoptimized, not even startup programs) runs way better than vista on my rig. Most notably when multitasking or when my PC has been on for a long time. And better battery life. Back then, vista was a disaster/dissapointment, even if it became so unfairly or undeservingly, and now the bad rep has stuck even if its fixed itself. 
I hope there are not green apples :shock:
