I was relying on Acer's statement that the version of 3.1 supplied by them does not support bluetooth mice, but what would they know.
By the sounds of it, a few people have had success with a BT mouse on the stock system, so maybe "not supported" means you could be lucky but if you're not don't complain to Acer.
Pete seems coy about sharing advice on how he got his Microsoft BT mouse working, so the best I have come up with is from Icebike at AndroidTablets.net who had success with a Dell BT mouse;
"I just had to unpair it to refresh my memory, Here's what I did.
Start by unpairing it.
On the tab make sure its discover-able and blue tooth is on.
Then pick up the mouse, turn on and tap the blue button.
On the tablet, in bluetooth settings scroll all the way down to scan for new devices.
Select your mouse (by its mac address which is printed on the bottom).
Key in 0000 for pairing. hit ok.
Tap any mouse button and a cursor will appear on your screen.
Every time you wake the tablet, tap a mouse button to tell the tablet that the mouse is ready."
king12 - if the documentation with your mouse doesn't mention a pair code and 0000 doesn't work, you could try other typical variations like 1234, 9999