For what it's worth, here's a screenshot of CPU usage as I plug in my Kensington EDR Bluetooth dongle.
First 2 screenshots are for the Kensington EDR Bluetooth dongle.
It maxes the application CPU, which then drops. Then maxes the system CPU and stays maxed.
I have a Socket Bluetooth (rev K) CF card also.
The 3rd screenshot shows the CPU in sysinfo as I plug in the Socket Bluetooth card.
EDIT: The CPU usage for the Socket card is quite a lot lower than the above USB dongle.