[riffraff]

IME using any value as boolean never caused me any problem, neither in ruby nor in other languages where the same is possible.

What stuff should happen when something is unexpectedly nil if you tested it for truth-ishnes? Once you have written

    if not some_value
      something with some_value
    end

the only things you can do with `x` are things you can do with `false`, which are not many.

[Confusion]

See my response to necubi. The main problem is the reverse:

  if some_value
    something with some_value
  end

where you first use nil to signal false, but later change the base case of some_value from nil to 0, nil to NullObject or nil to some other base value. Since you think of these base cases as 'nothing', you will forget to change this related conditional the first time around, because it seems it would still do the right thing.