I have an HP DC5800 SFF running Vista Ultimate. Every time I stop using the computer for a few minutes, it will hang when I return until the USB hard drive attached spins up. It must be using it to write temporary files or something, but I don't want it to. It doesn't matter what drive I attach (I have about 4 differrent makes and models), it does it to all of them, and I don't have speedboost turned on for any of them. Most of the time I notice it when using Outlook.