This is what NIST says about it[1]:

    Advancing technology has created a situation that has altered previously held best practices
    regarding magnetic disk type storage media. Basically the change in track density and the
    related changes in the storage medium have created a situation where the acts of clearing and
    purging the media have converged. That is, for ATA disk drives manufactured after 2001
    (over 15 GB) clearing by overwriting the media once is adequate to protect the media from
    both keyboard and laboratory attack.

That's an elaborate way of saying that zeroing a healthy modern disk is sufficient. No need to break out the crucible or jackhammers. If you really need to indulge your paranoia then use some wiping system that does multiple overwrites with random data. It's not necessary, but at least you won't put your eye out.

[1] http://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublic...

If the device isn't healthy and can't zero all of the media then you will need to resort to physical destruction.

Yep. You can over write it once with zeroes (or random) and you are done.

Right? What are the people in this thread doing that they're worried someone would take the time to employ theoretical, if not entirely hypothetical, recovery methods against a zeroed disk?

Zeroing out a 4tb drive takes some time. Sometimes you might be in a hurry ;)

That's fair, but that doesn't explain the people talking about 10 pass overwrite routines and other such nonsense.