MY Personal experience with Vista
I have used Vista only on friends' computers, so no real-life, day-to-day experience with it, but I have been using Windows since 2.5, up until Vista was released, so I believe myself to know a few things about the Windows series of OS.
I ran the initial start-up and installation of my grandfather's Vista-preloaded computer. I have done quite a few of these during the years, and the comparison with other Windows versions was not promising. It took forever. With XP I have done quite a few clean installs and initial start-ups, and it usually takes an hour (clean install) or about 20 minutes (initial start-up). Vista took two hours with an initial start-up.
Later, he needed help, because despite the UAC, he had managed to do some minor damage to his system. Minor because he had only disabled one application. All the rest were running (slowly, but) happily along. In XP I know the ways to correct this problem, and it wasn't TOO different in Vista, but as the layout has changed completely, and settings have changed categories, it took me an hour locating the tools to perform the operations. XP would have let me at them after five minutes or less.
Having found the tools, I set out to correct the problem. In XP, I know the procedure well enough to know that it will take maximum an hour to run the tools. In Vista it took the better part of five hours.
He wouldn't even have been able to make this problem in Ubuntu. He would have been able to do it in EVERY Windows version out there, from as far back as 2.5
I have used a friend's ultra-lightweight laptop with Vista connected to a large widescreen TV as a music player. During the party, a few other friends with computer knowledge dropped in, and we wanted to check out some features of the machine, not the OS. We had to get to the Control Panel while playing music in iTunes. We hit the flag-button (Start-button) and waited. And waited. It took nearly two minutes to pop up. We had given up already.
An ultra-lightweight laptop provided by a school in a poor district isn't exactly what's recommended for running Vista, but come on. You play music and then it takes two minutes for the menu to appear? XP might have been sluggish on that computer too, but I doubt it would have used two minutes to open the menu.
From a side-experience, I had a very old laptop. Comparative in size, but not specs. It was a Pentium 366MHz, 192MB RAM, 6.2GB HDD, no graphics-card, integrated sound, no network adapters of any kind, 1xCD-R (my father almost chose floppy for this computer more than eight years ago), and 1 USB 1.1 port. It had XP on it, and did a fairly good job. (Compared to Vista on the laptop above, it only took five seconds to open the menu). I decided. after getting a DSL-cable modem with USB connectivity to try going online. I had to search for almost six hours on another computer to find a driver allowing me to do that.
Having another computer working perfectly with XP, and only curiosity to see what the laptop could do, I tried Ubuntu 6.06. I installed in less than an hour, was online (found the USB-port and ticked a checkbox to tell the OS that it was supposed to be used for networking) and finding that the only thing my desktop with XP could do better and faster than the out-dated laptop was viewing YouTube videos. And that's not a very crucial part of my online-experience. I stuck with Ubuntu. Since then, I have upgraded to 6.10 and sold the laptop, gotten a modern laptop, installed 6.10, upgraded all the way through 7.04, 7.10 and now 8.04. Only trouble so far has been with widescreen in 6.10 (solved in 7.04) and wireless in all versions (ndiswrapper needed to use native Windows-drivers in 6.10 and 7.04), but in later versions (7.10 and 8.04) it's just three mouse-clicks to get it working perfectly. (Broadcom doesn't support Linux, and therefore the three mouse-clicks)
A lengthy post, and one filled with off-topic references at that. But these experiences are linked together with my experience of Vista in particular and Windows in general.
A final off-topic experience: I had to do four clean installs of XP on my modern laptop in less than 8 months. It took me nearly a week getting everything back to the way it was, every time. I have tried a few distros on my laptop, and the clean install of Ubuntu and getting everything back to the way it was, has never taken more than six hours.