I have read some comments of some users saying that Vista runs slower than XP and that's not my experience when I use it in my eo v7110. The only problem with vista in that unit is that you wont have any way to use Media Center or WMP to play video. Well, a friend of mind at todoUMPC.com created a little tool to run some graphic benchmarks in his Asus R2H. His tool creates 500 Sprites (64x64 px) rotating simultaneously in the screen, with alphablending and shadow. He tested the machine in two modes, using the Power Saving feature when running on battery and using the best performance power profile while connected to power. And here are the results:
.Power Save - 5/6 FPS
.Super Performance - 43/44 FPS
.Power Save - 13/14 FPS
.Super Performance - 44/46 FPS
As you can see, Vista has a better graphic performance than XP. One interesting point, the result when the test is run on battery shows Vista with 2.5 better performance than XP, and this probably shows partially why the battery life shorter than what XP gave. The Power Saving Profile in Vista has been tweaked to have enough power to guarantee a good overal performance running Vista.
Of course, the overall machine performance is not just dictated by the graphic performance but it plays a very important roll on it. In my experience if you disable many of those fancy features of Vista, this OS works as well as XP in UMPCs using Intel processors. I do not say all UMPCs because Vista processors do not support some DirectX features and as result the graphic performance in these machines is not good in certain tasks.