I'm curious as to what you mean by overall performance. I'm assuming, startup, and generally browsing in windows. I certainly find no lack of performance in this regard...I'm always puzzled when people bring this one up.
I've liked Vista for 2 years...I think if it pissed me off as much as ME did I would have noticed by now.
Well, for example last night I had some friends over. We wanted to pull up a video on youtube, so I launch firefox. Which takes a few seconds to launch, and then a few more. Not noticably faster than XP at all. Then when loading other web pages it loads super slow. I have 4 gigs of RAM and a 20mbit internet connection and can download torrents at over 1MB/s (that is mega bytes). So I know its not my network.
My G5, my Macbook Pro, and my 4 year old PC running XP runs just as fast if not faster.
I was playing the Left 4 Dead demo the other night and it crashed, and I noticed steam was taking up 3gigs of Memory. I had to reboot to clear it.
My machine idles at 1gig of RAM in use, which is fine if Vista actually took advantage of memory caching, but it doesn't; or if at least it does it doesn't do it very well. Programs like firefox should have needed library files preloaded in memory if I use it a lot, and I do, and I assuming that Vista does since it uses about 25% of my RAM when idle. The whole concept of the RAM caching is that RAM is very fast and readily accessed over virtual memory (hard drive) and unused RAM is a waste of RAM. Linux, Unix, and OS X all do this too. They will cache out things to unused RAM when you aren't using RAM to boost over all performance. Yet my 4 year old PC, running vista, heck I'll just list the specs
AMD 3400+
Asus A8se Mobo (I think thats the model)
2 Gi DDR 400 RAM
Ati 9800 Pro 256MB
That machine running XP surfs the web at the same or greater speed than my Vista box which has the following specs
Intel Q9550
Asus P5N
4Gi DDR 1033 Corsair RAM
Nvidia GTX 260
SATA 2 - 32MB Cache Samsung HDs
Now, if Vista was really taking advantage of the 64 bit memory addressing, the memory caching, and preloading needed instruction sets and library files that I needed to surf the web, it should run a whole lot faster.
It doesn't. It offers no overall performance increase period. What it does offer though is better gaming performance but only because I have lots better hardware. I think that if I loaded XP Pro SP3 on my new rig I am sure games would run the same on my system.
So what am I paying for when I upgrade to Vista? A new pretty interface? yes, that is a great feature and I like some of the interface changes in Vista. I think that intuitiveness of the interface is a great factor in an OS. Vista trumps XP on that for sure.
What I don't like about Vista is that it supports newer and greater technology but there is not performance increase to be had, and it requires a lot more hardware to run in the first place.
Major Linux distros get major overhauls every 6 months, so you won't see a huge performance increase from version to version because they are updated so frequently. Jump a whole series of versions and there is a noticeable difference. OS X, gets a major OS update around every 18 months or so. OS X 10.0 came out in likw 2000 to 2001ish and now in 2008 we are at 10.5.5. You still see performance increases, and my old Macs run Leopard pretty darn fast.
Now, with Windows it takes them years and years to release new versions. XP over 2000 was indeed a noticeable performance increase. The hardware requirements were a marginal increase compared from XP to Vista.
Overall, I feel that Vista has the potential to be faster than XP, but doesn't take advantage of its new technologies to make it worth the upgrade as of yet. Which means there is very little point into having it, unless you want DX10, which is what I wanted so I loaded Vista. I can't say now that it is worth it just for DX 10, because I don't feel that it is really that much greater.