Here in FL the law, unless I'm remembering it wrong (though I'm pretty sure I'm not), requires that your bike be "equipped with a brake that allows the rider to stop within 25 ft. at a speed of 10 mph on level, dry pavement."
I don't use a brake, though, and where I live fixed gears are such a rare sight that I've never been approached by any LEO's to prove it; I've never tried it to see if I could. They are much more likely to stop you for not having a light at night.