hansb,
I have been trying to solve the exact same problem with regards to flash drives for a while now. The 'hal daemon' is indeed responsible for the mounting of external devices. I have a 2gb fairly cheap and nasty mp3 device that has never 'hot plugged'. I know through my research that it is far better to have such a device formatted as fat16 as opposed to fat32. I can't recall why this is but will have another search for you.
I have come across many different elements to the subject of hotplugging devices when searching for an answer to this problem. it confuses the hell out of my humble mind.
http://www.lockergnome.com/nexus/linux/2…otplug-devices/
might help but I am unsure of it's contemporary relevance
https://answers.launchpad.net/ubuntu/+ticket/3425
Is the closest I have come to finding out what is wrong with my hotplugging. Personally, I imagine it is possibly down to my hardware.
However, when I enter the bios(press f2 when first screen appears) at boot I notice a message which says 'usb device initialized'. Maybe this is overriding any device I choose to plug post-boot? I don't know for sure. I do know that this problem remains for me.
Lastly, have you looked through the output of 'dmesg' after plugging the device? It may tell you something.
Entering 'lsusb' in a terminal will list all of your active usb ports and any devices which are plugged in.If you can see your device after plugging it post-boot with lsusb you are getting somewhere.
I would suggest posting a thread at launchpad if you can't solve this problem through these or any other forum.
good luck
dkaddict