[ALUG] automount of USB drives not working - where should I look?

I've just discovered that automounting of USB drives isn't working on my xubuntu 11.10 system. I can see the device with lsusb:- Bus 002 Device 005: ID 0951:1607 Kingston Technology DataTraveler 100 but no sign of it automounting. The "Mount removable drives when hot-plugged" setting is ticked and it always used to work (though I'm not absolutely sure it has worked since I upgraded to 11.10). Any ideas? -- Chris Green