They run the SC Single firmware. They should ship with version 1.2.5, which is the newest.
The only tweaking I've seen were done on Jalapenos, where some tricks transfer over to the SC Single, and some don't. For the Jalapeno, there have been 2 big ways to increase hashrate: Flash a newer firmware, and then put the Single in a freezer before you start it up.
The BFL ASICs do a sort of self-diagnostic every time you power it on. It's got 16 chips, and each ship has 16 cores. Most chips only enable 14-15 of it's cores, and some might work at higher speeds than others. To increase your hashrate, you want to first of all increase the number of cores per chip you're running, and then increase the hashrate they're running at. You might get more HW errors with both of these improvements, but the overall hashrate will more than compensate for that.
For Jalapenos, they come with Firmware version 1.0.0, which limits you to 5GH/s. Flashing them to 1.2.5 gives some substantial performance boosts, enabling all available chips/cores at a safe frequency. The Singles come with a stock version 1.2.5, but there's still some room for improvement. You could try flashing Ckolivas'
modified 1.2.5, which should be a little better at enabling questionable cores and/or running them at higher speeds. I don't know of anyone who's done this on a Single yet, so who knows?! You might brick your device, I'm not sure.
The second trick is to put the Single in a freezer for a half hour before you power it on. Don't run it in the freezer, but just get the chips nice and freezing cold before you turn it on. When it does that self-diagnostic test, you might get better results if the chips are 0C rather than 25C. Of course these lower temps won't last long once it start mining, but it will be mining at a higher clock than it was, and it will give you more hashes. Again, you'll prolly get more HW errors, but it's probably worth it.
I sold my Single, and the guy said he went from 57-62GH/s just by using a different PSU. I'm not sure why that is, as it was getting the same 57GH/s with the BFL PSU, my Seasonic X-650, and his Antec 900W one, and finally when using it with a CX430, it went to 62GH/s. No clue why, except for many the self-test decided to play nice and give him good results.
TL:DR You could try flashing a modified firmware, but that's quite risky. For low-risk, put it in the freezer for an hour before you power it up and mine with it.
