Just one trade so far:
June 17, 2011, 3:32 p.m. Obtain: 19.5000 USD Gave: 1.3000 BTC 0.1053 USD Commission
but plan on trading a lot more.
I'd say this is a bad deal for the original poster and a great deal for everyone else. I have gotten 79 referrals since opening day and it has netted me only $2.61 so far.
It's the OP's gamble, and yes, he will need big trades happening to make his btc back. (I thought the revenue was about 10% of a ~0.50% commission, at which rate it will take him 200 btc ~ $3000 worth of trades per account to make his money back)
This is not a sum that's likely to happen for the average account anytime soon. However, what if one of his referrals is one of the old miners, or someone who decides to go daytrading with btc or someone who decides to store his savings as btc. Or, if the exchange lives up to its ambitions and btc does take off in a big way, this might actually be a reasonable return for an average account.
Yes, I guess it's a big gamble, but no-one knows where this thing is going yet.
I say it's up to everybody individually to decide which gambles are worth it, and which ones aren't.