Hate to be posting this (especially on Pi day!) but here are my results of using the Pi with 17 miners.
Getting the Pi working was a breeze! Simply loading the OS (Raspian) and logging in through SSH (after the initial menu config) allowed me to compile cgminer just like on Ubuntu server....although a LOT slower.
After modifying the text file for stability (as posted in this thread) I fired up cgminer and it started hashing. Things were looking good and I was elated so I went to bed. I did notice that on the Pi cgminer takes from 10-25% CPU sometimes shooting up to 50%. Figured that was fine as long as the little guy was working.
Little backstory. Before using the Pi I was successfully mining using a ThinkPad laptop with Ubantu server. I took two screen shots in 24 hour intervals on that computer. First was at 800 and the second 850.
Back to the Pi...so I woke up and checked in on the Pi. Was disappointed to see some of the miners were not hashing as fast and that the average was low. HW was also MUCH higher.
Left it hashing and went to work.....checked on the pool to see how it did overnight...not good:
You can see where I started to use the Pi at around 2:00 AM. For some unknown reason it went WAY down from around 5ish to 8ish. Overall the hashrate looks lower than the Thinkpad.
Will keep it running on the Pi for another 7 hours but thinking that the Pi will be going back to the store. I'm sure it beats using the controllers but perhaps it's just not fast enough.
I'm running 19 miners currently on the Pi and it has not had any stability issues. As you can see in the screenshot below, system load is under 0.1, cgminer processes are mostly sleeping. Some differences from your setup: 1) I'm using scripta and a precompiled cgminer posted by someone initially on litecointalk; 2) I'm running two separate cgminer instances (10 and 9 miners). I would suggest for you to try the precompiled cgminer and see if that performs better. If that doesn't help I would start narrowing the problem by disconnecting half of your miners to see if there is one malfunctioning device that might be causing cgminer to misbehave.