In fact this was working in 11.04 untill some updates were done for the linux itself.. I'm not aware since which update this problem was caused. Yes, the problem also exists in 12.04 but not with UNO (they did have a problem for UNO regarding some 'upowerd' which was polling the usb..but that was patched). This problem is only for older Arduino boards.
If any idea which update might have caused this problem, it would be great!.
Also, it seems that in 12.04, the Arduino NG sometimes dosen't boot the program written onto it when connected to the serial port.Its as if the serial port has a lock on the Arduino. 'lsusb' and dmesg does not show the port being used by any other software.
I'm pretty sure this is cause of an update on the serial port. Any clues?! 