I have a 100 % cpu utilization when I enabled usb 2.0. I run Windows XP sp3 as guest on a openSUSE 11.0 host. Without usb 2.0 the host the cpu is about 30%.
I have installed this version: VirtualBox-2.1.4_42893_openSUSE110-1.i586.rpm
The virtual machine runs in ASPI mode.