We have two laptops in the house. One is an Advent that the other half bought without asking me about laptops first (need to stress that part haha). The other is an MSI GT725 gaming laptop.
Both have Vista and all I can say is the performance is at polar opposites. The Advent is sorely lacking in ram which makes the whole system a complete waste of time. My quad core laptop runs smoothly and like a dream to be honest.
By all accounts Windows 7 is less resource hungry but this is only really noticeable with the machines that were lacking in power to begin with. In short, Id likely see significant improvements on the Advent but would see very little on the MSI.
I would like to upgrade to Windows 7 but having spent the whole weekend trying to get my Readynas Duo, iTunes, and the Squeezebox working I dont know if I can be hooped going through that again!