In a very recent CAP inspection for IHC, I was asked that question, I use an 
automated system and run 1 monoclonal antibody negative control and 1 
polyclonal 
negative control per run, also all my positive controls have negative areas 
and the inspector said "I covered all the bases", I can't say every inspector 
will be this generous, it seems ridiculous and costly to run a negative for 
every antibody, unless you are totally manual.                         Dana