It's funny how much discussion, spam, and links there have been for tradehill referrals given how little they actually matter. In total tradehill has done $1.25M in trades x .6% = $7,500 in revenue x 10% = $750 in commission. Not sure if I'm missing something, but $750 split 20,000 ways is none too exciting.
The fee is 0.5% on each side, so it's 1% in total --> ~12500 USD, ~1250 USD in referrals and of these ~16.50 USD are mine alone.
@OP: Honestly you probably anyways don't trade enough to be relevant for anyone referring you - just pick a code and sign up to get a rebate, I doubt you'd get 1 BTC or something as a reward, only people begging.