i render to openexr, which uses 32bit floating point numbers for rgba. gimp's current stable releases are (afaik) still limited to 8 bit integers for rgba, so it's not an acceptable option for me just yet. this forces me to use proprietary image editors, which is regretable.
it sounds like gimp will soon be able to handle such formats, at which point it will become a valid part of an industrial toolchain. i can't wait. :)