Relax, gasman. I actually got a pretty good chuckle out of some of the remarks that were made. Loosen up.
Is secondhand smoke beneficial to a tank? Obviously not. Is it harmful (your original question)? THAT is very debatable and a very valid question.
Most purists will undoubtably tell you that ANY contaminant is harmful. reckler has no problems with his/her tank.
I really don't have an answer, but I do have some insight. As with any contaminant, observe how many opportunities your tank has to get maximum exposure from cigarette smoke. An open top tank will absorb "some" smoke- air isn't heavy enough to break surface tension effectively, but smoke is heavier than air. If you run any air pumps or venturis, the smoke will get directly injected into the water.
I'm sure that someone will support the argument one way or the other, backed up with data.
Until then, try to SMILE.