Seems to me, most people hate on vista just because that's what "everybody" does. There seems to be few to no rational reasons for it.
I have XP on my work laptop, Windows 7 on my desktop, and my wife has Vista on hers. I had Vista on mine also but bought it close enough to Windows 7's release that I could upgrade for free.
There is a big rational reason for hating Vista even now, although it has been patched up a fair bit and it is fair to say that I would probably pick Vista over XP now if I had a choice. But initially the user interface was laggy as hell (that was only fixed in one of the service packs). The default settings for stuff like icons meant you get huge icons, and a lot of them, with no visual text indicating what they are - say you had a card reader, then all the ports would show up as huge identical icons and you'd have a tough time even picking out your C or D drive, let alone the drive that actually had a card, and you had to scroll through them because they were so ridiculously huge that only a few fit on the screen at any one time.
You could fix a lot of that manually, but that was tricky to do and even trickier to find out how to do it in one setting for all windows (I'm still not even sure anymore that was even possible). And then of course there was a long line of driver hassles, which in our case meant we were not able to hook up our scanner. A new driver was promised but never came, and a universal scanner driver like Linux has never made it to Windows for some reason.
That's just some of the frustrations we had personally. At work of course stuff like the initially somewhat clumsy UAC and DEP implementations were a hassle as well. They would be good if software vendors were prohibited from releasing software on Windows that don't support it properly, but alas, plenty of high profile stuff we sell still requires turning that down or off (oh and suck you .NET Framework for not working with paths longer than 259 characters).
Make no mistake, I like Windows 7 a lot and think Office 2010 is pretty good too. But it took a good while to get there. I'm happy Microsoft gets a little more serious competition these days in the desktop space, even though it is still marginal.
What they really do is having different licencing models. If you want to get it cheap it's stuck with your motherboard and is hard to move to new one. If you shell out more cash you can get a version you can install on any PC you like.
Doesn't change reality - you cannot get a single machine license for cheap. Upgrading my wife's computer from Vista to Windows 7 costs half of a new PC.