Hmmm... what people don't seem to realize is that they want Vista largely because it is a newer code base that is easier for them to secure.
Ignore UAC, which by all accounts doesn't do much good. Then we have the controversial locked up kernel (which they then relaxed a bit).
But what they really have in Vista is an attempt to stop running stuff as Admin. Unfortunately, programs are stupid and suck and demand administrator priveleges. What MS should have done is to include the desktop virtualization tools they bought from Softricity by default (or rather, a small portion of it). That would allow apps to run thinking they are running as admin, but without actually being so. Some things wouldn't work (an app can't place itself in startup), but most others would. (If you don't know what the Softricity tools are, the best comparison I can offer is that of the isolation mechanisms of BitFrost though the focus there is a bit different, and they don't have many of the abilities, or indeed the need for the abilities of MS's product).
Plus, if you have seen the driver programming model, you'll realize how much it really helps. Believe you me, writing drivers for Vista should be much easier.
End result - Vista will replace XP eventually. Most people buying new comps will go the Vista way. And MS will quickly change portions of Aero to make it a productivity enhancer, rather than just a skinning interface.
