I think I have said it once or twice -- but merely to warn folks not to get too discouraged when trying the process for the first time. Actually the opposite is true -- large areas of smooth tonality will quickly point out any sloppiness in one's process.
Incomplete or uneven mixing of the pigment in the glop
Excessive graininess caused by poor pigment choice (particles of carbon too big)
Beard hairs, dust, etc in the glop
Defects on the neg
That is what I can think of right now.