Was flat when it happened, and don't trade YM.
For the CBOT it was a slip-up, and it's not surprising that they would bust trades off such a huge move. Fair is another thing, though, and they really should have circuit-breakers against moves like this - so that everyone knows ahead of time where trading will be stopped. Explicit, precise rules about when and how trades will be busted would also be helpful. (If they do exist somewhere, maybe they need to be more broadly publicized.) Everyone does know pretty well though, by now, that if a big player hits the wrong button, he gets taken care of. If one of us normal guys hits the wrong button... we hit the wrong button.
The traders who made what they thought were good, opportunistic longs on the counterreaction, then closed, but, after the trades were busted, found themselves short, should arguably be aware that conventional trading rules don't apply on totally out-of-the-envelope moves. There's a difference between reflexively taking the other side of an exaggerated move and rushing in when something is seriously out of whack. When an index futures contract moves 6% in less than a minute, any trade you take until things are sorted out, or at least until you know exactly what has (or hasn't) happened is pure gambling.
On the other hand, for the other indices the event was similar to a big news headline or rumor that turns out to be inaccurate. After 9/11, for instance, we had a few big reactions to news headlines that on further analysis turned out to be overblown or entirely bogus. Arbitrage creates a more intimate connection between all markets, making this case different, but the principle remains the same (though not the principal).
To me, the way Globex and the brokers handled the outage a couple months ago was at least as unfair to small traders. How open positions were going to be handled remained a mystery for hours, and there was much misinformation spread around.
Situation normal...