I bought a new PC a few months ago and it came with Vista64, is has an Intel 2.6G quad core and 4 gigs of DDR3 ram, dual 500G SATA2 HDs. I came with an Nvidia 8500, but I upgraded that to an 8800 for gaming.
I am MOST pleased with it's performance, everything is fast, I have never had a faster machine. I guess Vista had many many issues when it first came out, but it is as solid as a rock now, I haven't had a crash yet.
Most of the controls are fully intuitive, but i did pick a book on it.
The few drawbacks are:
You have to learn to run some program like A1 cleaner as an administrator, but thats easily done.
Office 97 doesn't run on Vista, so I had to spend $100 to get office 2007, and learn about it ... not too bad really.
My recently registered copies of Webroot's Window washer and Spysweeper will only run correctly on Vista32
Many companies are working on Vista 64 bit compability, but they also seem to be dragging their feet. In a way Vista64 bit is still for pioneers.
But A1 cleaner and RegVac both work perfectly fine.
So if you can live with these minor issues, go ahead and do it, for all of its' bad publicity Vista is Sweeeeeet!
If your lagging a little now you may benefit with more ram, XP really only uses 3.2 gigs of ram at the most - You wont do any worse switching to Vista