The big thing that makes Vista run slow on machines that aren't above average in power is the superfetching service, which you can read about here.
http://www.brainbath.org/toybox/free...windows-vista/
It can be beneficial if your system is robust (8GB memory, for example), but a hindrance if not.
Current Vista users experiencing poor speed, try turning this off in your services control manager, and observe the difference in memory usage and general speed.
Again, not a MS lover here, but I think many will find this to be a big help.