Pretty much nothing.
It is XP with a moderate GUI overhaul. They have changed/added some wizards and annoying UAC for "security". It is quite clumsily thrown together and a lot of programs do not work or will require you to purchase a new version of them. If you want the Aero interface [the only real noticeable change other than removing a ton of configuration options or hiding them deep within some wizard] you will have to pay for one of the premium versions and quite possibly upgrade your PC for it to run smoothly.
Seriously, it brings pretty much nothing to the table. I would really like to hear from someone actually running Vista that thinks it is a major improvement and most importantly why because I've been running it for a few months now and really nothing impresses me. They did upgrade solitaire I guess, thats worth $400.
Well I have made the upgrade, and I will chime in.
Obviously the biggest reason to upgrade is Security. The fact that the products that come with it, (Windows Defender, Firewall, UAC) are all pretty much configured to work for you out of the box is a HUGE improvement over XP. In XP, the firewall is only one way, whereas Vista blocks both in and out. Defender would have had to been downloaded, installed and configured, and UAC didn't exist. Protected mode for IE7 is the bomb, and unfortunately not available for XP (due to necessary file system priveleges that can't be made available), which essentially ties IE into a program running with much fewer rights than most others.
I welcome having Windows Update (or Microsoft Update) available via the Control Panel. This now means that there is no need to use a browser for it, and should cut down on installation problems.
Parental Controls is amazing. I haven't had much time to play with it, but I have already set it up and it's running at my parent-in-laws house, restricting time of Internet Access per the accont as well as blocking certain games on the PC during times when they would prefer their younger siblings doing homework. They didn't specifically request it, but I figured I would pitch it - it works like a charm and they are delighted. The addition of being able to read instant messages was very nice as well, and actually provides some peace of mind because they know their children are a bit more protected since they can review online activity and adjust as needed.
Another aspect I tend to like is performance. I think my machine, on the same hardware that I ran XP with, runs a bit snappier even compared to a fresh install of XP (else an argument could be made that my previous XP install needed a fresh start).
There are also tons of nifty features, I really have grown to like the Live Taskbar Thumbnails that give you a preview of whatever window/application/file you have minimized.
Indexed search is a nice addition - I know there are comparable programs out there, available on XP, that could do the same job (some of you will also probably say better), but I really like how this instant search performs. The ability to customize what is indexed is also a nice addition so you can control the constant thrasing your HD does.
The Start Menu is much cleaner, more organized and easier to navigate. One of my favorite parts of that design, if you actually miss clicking on the "orb" to the left of it, it will still pull up. Microsoft actually seems to be paying attention to what could have otherwise been a brutal design flaw.
From a traveler's perspective, I think it's neat you can display up to three different times for different locations you may care about, all without having to think about it :
I could go on and on, some will hate it and some will love it. From an end-user standpoint who may not be as up to snuff with computer technology, the quick sales pitch to upgrade is Security - period. You simply can't compare XP to Vista with regards to Out-of-the-box security that it comes with.
-edit-
Also, for those of you who want to know more, you should read the review that Paul T has been working on -
http://www.winsupersite.com/vista/
Information there is great, I can't wait for the next installment
🙂