Going to try and set this up with 10 BFL singles tonight or tomorrow. I'll post back with results.
Well, let me know if it works for you. For me two work great, three feels like a spinning top, seems to get unresponsive after a while. When I start cgminer it sometimes hangs when starting. I am able to CTRL-C and it will quit. Restarting it and it's good for a while. It's seems that if it's over an hour or two any changes will make it "hang", like enable/disable a pool. I had three running over 48 hours, but as soon as I did something to it, bam... down like a domino. So since I had more Pi's I just put two on each. Also, the 10 port USB hub that worked great on the PC was not happy at all on the Pi. Strange... still tinkering with it though.
It's still awesome to see three little black boxes (2 BFL, 1 Pi) generating ~1.6GHash with such little power and heat. I hope it will run a Jalapeño or an SC Single.
Also, if you are looking for a great case for the Pi this one is very nice: (Have 4, work great, quality)
http://builttospecstore.storenvy.com/products/404262-raspberry-pi-enclosure-kit
I prefer either that case:
https://www.modmypi.com/shop/raspberry-pi-cases/raspberry-pi-case-white
or that case (which I use):
http://www.shapeways.com/model/486999/
The Pi should be able to handle a large number of BFL Singles, if you use 'top' to look at CPU usage, there should be no more than a few percent usage for 1 or 2 Singles.
Some people have reported that certain USB hubs seem to give hardware issues.
One thing I noticed that pushes CPU load to 99% is trying to redirect stdio (e.g. using the '&' operator) to /dev/null on cgminer.
But the mere fact that you have several Singles mining should not be the issue.
@Jezzz: Thanks for the test results, that's great to hear!