The acerhdf module, to control the fan on Aspire One netbooks, can also report the CPU temperature, but only if THERMAL_HWMON - "Expose thermal sensors as hwmon device" is activated in the kernel, which it isn't in the current Arch kernel.

To expose the THERMAL_HWMON option, THERMAL and HWMON need to be the same, either both as module or both built-in. But the Arch kernel has HWMON=m and THERMAL=y. Please set THERMAL to =m and then activate THERMAL_HWMON, so that it will be possible to read the CPU temperature on Aspire One netbooks using lm_sensors (and other applications using the hwmon interface, like Conky).