Hey,
thanks for the advice on the power supply. I got mine built and I'm only seeing around 60% efficiency when boosting from 5v to 170v (5v 170mA in, 170v 3mA out). I'm going to rejigger the circuit so that using 9v won't fry the attiny and see what happens then. It also seems that I can't get more than 130 volts with a 28000 ohm load, but this may be due to me capping the duty cycle at 98% (the attiny automatically adjusts duty cycle so the output is 170v). I'll work on it later today.
Edit:
GAHHHHH. I feel like screaming. I've spent the past five hours wondering why the #^%$ my boost circuit was only putting out ~70V after I tried to get it to work with 9V in. I proceeded to completely disassemble my perfectly soldered and very small boost circuit in order to exhaustively test every single component-of course, the component that had failed was the VERY last one I tested, and I only even tested it as an after thought. It was the output filter capacitor. There was no reason that thing should have failed, it was way over the required voltage rating. So now I have to re-assemble everything, and I'm out a really big filter cap. I almost trashed my inductor.
To anyone considering building a nixie clock, I HIGHLY recommend not building your own power supply, LOL.
On the plus side, it now works perfectly and holds stable at 9mA draw (set to regulate at 170v).