Care to elaborate? If your hardware is up to par, Vista will run fine. If you buy a retail machine, such as a Sony, then it will run like crap because they load so much garbage software on them. Brand new XP machines had the exact same problems (the worst being Sony, the best being Gateway and Dell in terms of which ones run the fastest out of the box).
Believe it or not, my PC with a Core2Quad, 4gb ram, and Vista64bit actually runs noticably faster than my previous PC with an X2 4400+, 2gb ram, and XP Pro.
I bought the 4gb of ram for $99. There's no reason not to be sporting 2-4gb these days unless you're still sitting on PC133.
Vista also uses superfetch, which precaches apps and programs that you load frequently, which is why when you check memory usage in Vista, it might say you only have 6mb of ram free. It makes a very noticable difference for me.
That's not to say that Vista isn't without its flaws. I hate how slow files transfer over a network with Vista. UAC is dumb, and I have it disabled, but for people that aren't very computer literate, UAC can be the determining factor in whether or not a root kit is installed on their system.
I'm not advocating Vista, but it definitely isn't the horrible operating system that everyone makes it out to be. Most people just have issues with it because they can't get their 10 year old printer that connects through a serial port to work (HP has dropped support for many older printers in Vista to get people to move on), or they try to install some old software that wasn't meant to run on it. They blame issues like that on Vista, when it's actually the fault of the hardware and software developers for either not providing a patch for their software or providing drivers for their hardware. A lot of companies are just tired of supporting old hardware and software and are using this as a way to progress their customer base to newer stuff.
Anyhow, AOC runs leaps and bounds better on my Vista machine than it did on my XP machine. I wasn't a believer before, but now I am.