Well from my personal experience with SP1 so far. It is great. It has improved performance along with made Vista more Stable. I think they did a great job with it. More work has yet to be done as it isnt anywhere near what Server 2008 has shown me. But it is a step forward.
So far what i have seen is good. But i cant really tell as i dont use vista for many big things. PLus i didnt use SP1 for long, ive been using XP. But i think the problem where shortcuts always jump to the top of the screen on the desktop was fixed