With the release of Oracle VirtualBox version 4.0.4 , I was crossing my finger hoping that this issue was resolved, but apparently it is the same deal.
Problem: VirtualBox CPU usage goes crazy even though the guest is idle. The only way i can get it to calm down is to create a dummy guest machine and run it simultaneously with the main VM.
Here is a video that illustrates my point:
Hopefully this video above will give everybody a clear idea of the issue.