I disagree - XP was a great OS for its time, but I don't think it meets the 2009 definition of functional. Security-wise it's fairly primitive, the user interface is dated, it has no indexing and only basic caching, Explorer isn't very intuitive to use, you can't adjust volume by application, it's nearly two DirectX versions behind, the 64-bit version has inferior driver support...
With 7 running pretty well on older hardware, it's time to put XP out to pasture.
Security - I personally don't give moneys about security, and I don't think many other home users/gamers should either ( at worst you'll have to reinstall?)...
There are enough mods for the interface to make it like vista. And I prefer the XP interface than the 7 interface, I hate the fact that in 7, you don't even have all the sorting options on top when browsing folders, instead, you have to rmb and click sort by and then click what you want ( and it has the habit of not remembering I ALWAYS want to have ''last edited'' as an option in the list). The new taskbar may be handy for normal users, but not for users with 2 monitors/enough taskbar/screen space anyways, it's easier arranged in xp/vista when you have tons of apps open at the same time, which I always tend to do... Same thing with icons in the bottom right corner, now I have to go into the options to make (some of) them always show or have to produce an extra click to view them. Again this is step backwards in productivity imo, it should rather by default show all icons, and make you able to hide the ones you don't need, because usually, I need the majority. New gadget system is worse for dual monitor users too, they used to have their own dedicated space on my 2nd screen and when I did '' always on top'', they never sat in the way of other apps but I could always see them when gaming to monitor my cpu/memory usage etc, now they either can't be always on top, or they sit in the way of way app I have in fullscreen/maximized on the 2nd monitor, rather than maximizing and leaving the sidebar alone on my 2nd screen, now an app goes into the space of the gadgets and the gadgets hover over my app

I could go on all day about what annoys me and slows me down more in 7 then it did in vista but I have to go to uni now or I'll be late

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I always turned infexing off anyways.
Lack of superfetch is indeed a shame

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Isn't intuitive? What do you mean ?
Who cares if you can't adjust volume by app? Just turn up/lower your volume on your speakers, and important apps DO have seperate volume controls eg. WMP and Games ?
Direcx10, hardly a loss is it ? Dx9 in xp still seems to run fine fps wise compared to newer OS's.
Of course you wouldn't notice you never do a fresh install
Of course a fresh install would be faster though, irrelevant of the OS.