Acer A500 internal storage is not auto-mounted by Ubuntu
On Ubuntu, your device needs to be manually identified to the udev system:

As root:
Create or edit /etc/udev/rules.d/51-android.rules and add this line:

SUBSYSTEM=="usb", SYSFS{idVendor}=="0502″, MODE="0666"


Then:

# chmod a+rx /etc/udev/rules.d/51-android.rules
# restart udev
udev start/running, process 3793


This works for my Sidekick on my Ubuntu 10.04 system.