Personally I just didnt mind upgrading to vista due to its low retail price and the fresh new look. After a time you can get bored with the same OS. Vista actually made my pc feel like a new machine. Every build I have done over the last five years or so has always had the same OS. So although the pc was new and quicker than the old, it always looked the same.
Get board with the OS? its like saying you get board with a dvd player and buy a new one because you are sick of the way its facia looks (and possibly performs worse until a firmware is released), who really cares what the os looks like other than mac fan boys. I use the os for the applications that are built on top of it, browsing the web, watching videos, listening to music and playing games, how could any of those be enanched by the look of the os especialy the latter thats in full screen mode (taking out of the eqaution any potential visual improvement dx10 may bring for this paragraph).
If dx10 was on xp even less people would have upgraded to vista,but forcing people is in the short term knock credibility from dx10 in both users and developers eyes. And its not helped by the shoddy dx10 hardware, with dx10 ment to make devleoping easier, and the hardware more efficent it looks to be doing the reverse. DX9 and all that went before it were backwards compatable so developers made one game regardless of the dx version the hardware supported (latest or ancient), now they need to make 2, or 3 if they want to port it from xbox 360. Looks like the whole XNA idea went down the poo shoot just to stisfy some ms statistics with bolsterd vista sales. From the games that have came out dx10 support so far have had either dire dx10 results compared to the apparently less efficent dx9 or required heavy tweeking from the developer to bring it upto par. The visual results so far are practicaly invisible to the gamer who's actuly playing the game and not got two machines side by side to compare the difference between dx9 and 10.
So far we have dx10?:
on one os, and one thats not exactly renowned for its stability, support or general robustness.
the removal of backwards compatability, meaning that games on a tight deadline are gonna have to implement dx10 and 9 seperatly and so reduce other elements of the game.
Lack of uptake on the hardware side (mainly due to pap midrange admittadly).
In general a poor first showing for the revolutionary dx10 graphical euthora.
No doubt one day vista will be as rock solid like xp, it'll have all the driver support it needs and once developers get used to dx10, the games with the big budgets might start to show some real promise, and obviously hardware will get better. But if the majority of users stay with xp and/or non dx10 cards then the vast majority of games will have to be dual compatible and this might just kill dx10 or at least stick it in a comma for a year or two as game developers will go where the money and thats dx9 for the forceable future, at least till the next uprade cycle.
On a technical note it'll be interesting to see what dx10 can do that dx9 can't.
Back to vista in general over xp/2k, its much like ms office, they keep bringing out a new version but one from the 90's will have all the functionality your ever likley to need.