ssh to the unit's ip (using putty or whatever), pi/raspberry for user/pass.
cp ~/Garden/miner.php /var/www/miner.php
Then browse to
http://IP.OF.MINER/miner.php, this will show you a bunch of information from cgminer's API, including the error rate. I don't know what people average, but mine is showing 4.79% (listed under "Device Hardware%") running on stock firmware (0705 version).