Yes, I too have seen those spreadsheets, but it's not Excel that's at fault, it's the users. I've taken XLS behemoths and trimmed them down to a fraction of their size and optimised sheets that ran overnight, to recalculate in seconds. I get what you're saying about Excel giving too much power in incapable hands, but I feel, for certain use cases, OO is too little power in even the most capable hands.