I wonder the same thing. How can 7 random passes be any more secure than 1 pass with random 0's? This must be one of the IT worlds biggest (false) myths.

I mean, If there are (recoverable) traces of the previous data after one pass, how can I be sure that my newly written data isn't corrupt? 1 bit should be 1 bit, right?

Please, can anyone demystify this myth, or is it just something everyone accepts?