any 2.5x version of blender i have used seem to suffer from this. your working away and suddenly the keyboard is unresponsive, blender is running fine, just not recognizing keyboard input, switch to any other program and back and the problem goes for a while.
i have no other issue’s with my macbook pro’s keyboard so its not the hardware.
it seems completely random, i can pin it down to any particular act. its not during field input or anything, just general edit mode extruding, vertex pushing stuff.
just checked 2.57 from blender.org.
update on offending bug: blender accepts input in text fields but key shortcuts in 3d view don’t work. switch app and type anything, then back to blender and all is ok.