Precommitted to publishing this in Discussion to fight publication bias.  It looks like intelligence (as measured by IQ, SAT scores, etc.) isn't meaningfully related to how much one posts to LW.  Probably in the ideal case, they would be related and higher-IQ people would post more, but that doesn't appear to be going on either.

How well-educated you are doesn't seem to be much related to participation either.  I'm not controlling for hours spent on LW for any of this, though.

Script output:

Correlation between "IQ" and "KarmaScore": 0.0343
 
Correlation between "SATscoresoutof1600" and "KarmaScore": 0.0517
 
Correlation between "SATscoresoutof2400" and "KarmaScore": 0.1000
 
Correlation between "TimeinCommunity" and "KarmaScore": 0.1770
 
Breakdown of average "IQ" by "LessWrongUse":
  137.2500    "I lurk, but never registered an account"
  139.3659    "I've registered an account, but never posted"
  138.8491    "I've posted a comment, but never a top-level post"
  137.8182    "I've posted in Discussion, but not Main"
  138.9394    "I've posted in Main"
 
Breakdown of average "SATscoresoutof1600" by "LessWrongUse":
 1469.5495    "I lurk, but never registered an account"
 1462.1429    "I've registered an account, but never posted"
 1488.0000    "I've posted a comment, but never a top-level post"
 1510.2941    "I've posted in Discussion, but not Main"
 1515.1515    "I've posted in Main"
 
Breakdown of average "SATscoresoutof2400" by "LessWrongUse":
 2202.9848    "I lurk, but never registered an account"
 2242.7273    "I've registered an account, but never posted"
 2211.8000    "I've posted a comment, but never a top-level post"
 2244.5455    "I've posted in Discussion, but not Main"
 2212.7273    "I've posted in Main"
 
Breakdown of average "KarmaScore" by "Sequences":
    0.0000    "Never even knew they existed until this moment"
    2.4444    "Know they existed, but never looked at them"
   48.9677    "Some, but less than 25%"
  105.9658    "About 25% of the Sequences"
  280.6434    "About 50% of the Sequences"
  704.3240    "About 75% of the Sequences"
 1185.0264    "Nearly all of the Sequences"
 
Breakdown of average "TimeinCommunity" by "LessWrongUse":
   17.3262    "I lurk, but never registered an account"
   23.6875    "I've registered an account, but never posted"
   30.0064    "I've posted a comment, but never a top-level post"
   29.5035    "I've posted in Discussion, but not Main"
   44.9663    "I've posted in Main"
 
Breakdown of average "AutismScore" by "LessWrongUse":
   24.3504    "I lurk, but never registered an account"
   28.0526    "I've registered an account, but never posted"
   22.7227    "I've posted a comment, but never a top-level post"
   23.7917    "I've posted in Discussion, but not Main"
   23.7391    "I've posted in Main"
 
Breakdown of average "KarmaScore" by "Profession":
  200.9000    "Other "social science""
  368.1176    "Biology"
  898.8333    "Statistics"
  373.3000    "Art"
  441.0035    "Computers (practical: IT, programming, etc.)"
  193.5263    "Business"
  260.2281    "Finance / Economics"
 1129.8438    "Computers (AI)"
 1719.5161    "Philosophy"
  113.8507    "Computers (other academic, computer science)"
  351.9024    "Engineering"
  335.8081    "Other"
  531.9570    "Mathematics"
 2505.8571    "Medicine"
  393.6364    "Neuroscience"
   81.5000    "Law"
  530.1607    "Physics"
  498.2941    "Other "hard science""
 1033.7391    "Psychology"
 
Breakdown of average "KarmaScore" by "Degree":
  612.8599    "Bachelor's"
  503.3694    "Master's"
  195.7708    "None"
  241.7024    "High school"
 1484.6757    "2 year degree"
   77.9444    "MD/JD/other professional degree"
  389.4167    "Other"
 1099.7925    "Ph D."

Script source here.