Never came across this thread. Read the first two pages and I was shocked...
Pretty interesting to bump this today, as Mark was charged of embezzlement. I too wonder what would the reactions be today. I figure they'd be really different.
It's not so different today. During the brief August crash on Bitfinex down to $160 there were complaints that people's buy orders at $170 weren't filled. That's similar to Kevin's experience, although Bitfinex didn't let people have their lowball buy order coins then take them back. I'd be furious if I had $$170 buy orders on that didn't get filled. However, MtGox kept on trading afterwards, and likewise Bitfinex kept on trading afterwards.
To start off my reply I'd like to say that our knowledge of Mt. Gox today is very different than what they had back then and that might influence each and every one of our posts in the forum.
Both situations are a bit different as far as I can understand. Someone (hacker or not) put up a huge sell wall (of what were supposedly legit Bitcoins and not Goxcoins as later in time) that crashed the market. People had buy orders low, because you know, just in case (who doesn't have them?) and the user managed to put a low order just in time to get cheap coins. Why not? Trades were rolled back under the reasoning that it was a hacker who did it... But people had already bought the coins. I know that coins on exchanges aren't really ours, but people had legitimately put buy orders and bought the coins at the price they wanted. It's not the buyers and sellers fault that their systems were not secure enough, as we've been having proof of in the last few weeks, and it isn't the fault of the people who bought the coins that other users (might have) had weak passwords.
As for Bitfinex's case, the orders weren't even filled to begin with, which was different (although also the exchange's fault: the system didn't correspond to what customers were expecting).
I know it's hard to ask for these services to be 100% able to correspond to users demands... But we can't (yet) resort solely to face-to-face trading and we need online trading systems that are stable and correspond to the user's desires, and don't simply rollback trades on bad reasoning.
The only legit rollback I recall (at least in near past) was that one where there was a 0.8 fork, and even that one might be questionable by some. That was an honest and serious bug related to incompatibility and was fixed quickly without a big harm to end users, as far as I recall.