When attempting to shut down the virtual machine (from inside the guest or by clicking "Send the Shutdown signal"), or when performing "Save the machine state", the machine status becomes Aborted. I will attach logs, one of the Aborted result during "Send shutdown signal" and one from "Save machine state".
Similar symptoms were listed in #5042 and #4020, however these appear to be fixed since VirtualBox 3.0.8 (fixed as in now the machine saves state properly if no USB device is connected, where as in those tickets the problem occurred regardless of whether a USB device was present or ever attached). Many thanks again to anyone that worked on the fix so this at least it now saves state without USB devices attached.
I have only confirmed this bug with MacOS 10.5.8 host and Windows XP SP3 guest, but forum posts suggest it may occur in other situations, hopefully someone else will post a log also.