I'm using Vista for like 2 weeks now and I have to say I really like it. It feels fluent on my comp and everything I want it to do works well.
But, being a Microsoft OS, it still sometimes feels like it simply has a mind of its own. Namely, when I see massive harddrive-operation when the system shouldn't be doing anything. Of course, I went for the usual "suspects" and disabled background defragmentation and the Windows search and indexing. But that didn't stop the harddrive activities.
After using the built-in Resource Viewer of the task manager - which is quite amazing, informative and very useful! - and after consulting google with the results, I found the cause: Superfetch, some kind of prefetch or caching mechanism newly introduced by Vista to speed up the access or starting-time of frequently used files and programs. Problem is that if your frequently used files are very very largs - like certain games - then that process of creating the cache takes alot of time and resources aswell. Yes I know, the Superfetch runs on low priority in background, but we all know Windows: no matter how fast the machine, as long as it constantly accesses the harddisk like crazy, lags in responsiveness are to be expected. And those can be annoying when playing games or watching movies.
So, after disabling those services, my Vista doesn't torture the harddrive anymore - not unless I want it to. I don't need search indexes since I usually know where my files are at, and I don't see the use of having another caching-mechanism. I haven't seen any significant speed improvements when Superfetch was turned on compared to now, so as long as my system works as I want it to, I'm happy with that.