could be a few bubbles in the brake lines, or simply worn out fluid.. i dont have any problems, but ive been comptemplating flushing out my brake lines and replacing the fluid with new synthetic.. ive used ate and valvoline in the past in other vehicles with good results (and a mityvac transfer pump...i love that thing!)
be warned though, wear gloves if you do this..the new synth fluid will suck the moisture out of any skin it contacts like a bad horror movie...great for brakes, horrible on the skin, and even painfull...
so unless someone tells me this is a bad idea, ill probably include this in my next major service (as soon as i can make time, unkown service history and all.)

anyhow, bad fluid or a bit of air will make brakes "squishy" id look there first...