I discovered that my printer "bloats" traces by a pixel or so when printed, and my crude attempts at etching didn't result in traces that were the same width as designed. So, I added an option to the postscript HID that lets you compensate for these deviations. I.e. you can, at print time, make all traces/pads/pins/vias slightly thicker or narrower than "actual" so that the resulting board ends up with the right sizes.
I've put a calibration board file at http://www.delorie.com/pcb/ that has a wide range of tiny traces and gaps with various bloat adjustments so anyone who wants to can both calibrate their process and find out how small they can go before the error rate becomes problematic. There's a PNG of the board so you know what it's supposed to look like: http://www.delorie.com/pcb/bloat.png FYI I discovered all this with a 200x IntelPlay USB microscope :-)
