It hasn't affected my O date at all.
If you want to peruse my charts, I was sick November 2011 (cold - I even discarded one temp due to fever in the 2ww), December 2011 (cold), Late January 2012 (I think the chart was January 29, 2012 - that was a bad UTI and YI and on antibiotics) and this current cycle I have had a cold for the past week.