When the price was going up up and away I bet you were perfectly happy.
Now that it's returning to reality, out of the woodwork come all the people who want regulation by central authorities. It would be funny if it wasn't so sad.
I don't have an account at MtGox
Notice that it also include "Limit UP". This rule is not targeted at exchage price itself. It is to avoid wrongly triggered incorrect trades and in case the exchange do not have enough liquidity or processing power. Give it 10 minutes, the liquidity will recover, but let it go, the liquidity will get worse and worse due to the panic sentiment change, although no fundamentals changed the price would still hit zero, and trigger a serials of other events