Well, MtGox's coders seams to be down on math, here's what it shows for EUR:
Last Price: 2.75098 High:5.01 Low: 3.3 Volume: 431
"Last" is lower than "Low"...
Looks like a bug. If somebody found an exploitable error in Mt. Gox's multiple currency system and used it to make some money, that may be the cause of the huge volatility in the last few hours.
All it takes is for one of the currency prices to be a little off, and Mt. Gox can lose big. They're the counter-party in their FOREX transactions. Of course, when they lose big, they have been known to change their unwritten rules retroactively.
I'd suggest pulling all assets out of Mt. Gox for a while, just in case.