How many boards could be safely/robustly supported via USB daisy chaining per host [PC,Pi,Etc]?
I discussed this briefly with some people when the ASICMiner USB devices were announced, and there were a couple of people complaining that in their experience connecting 15+ devices via USB usually led to problems, even with high-quality powered USB strips. I have little experience in connecting lots of USB devices so I can't really say, but this might be something worth checking out for users that are aiming to have lots of boards.
It is, in a word, horrendous. I have 18 CM1's connected to 3 7 port hubs, and it's a wiring nightmare. If I had purchased their stacking kits it would not be quite so bad as I could zip tie the bundle to some sort of post, but I wasn't interested in paying that much for 4 pieces of plastic.
I believe 8-12 boards may be daisy chained to a single USB before signal degradation comes into play, though Bkk should probably confirm that.