Generally: +1 on making sure examples in the docs are up to date.  If someone wants to do the tedious work of making sure that a "make doctest" succeeds, I'm all for it, it may involve adding a few (in HTML output invisible) testsetup blocks.

Eric: I'm not sure what the difference between your methods 2 and 3 is :)

As Terry already mentioned, by far not all example code is covered by that, and I don't think there's anything we can do about it.  We can of course try converting more doc examples to doctest format, however:

a) for longer examples and especially function/class definitions this really hurts readability and usability (think copy/paste)

b) many examples are also not easily runnable (Tk is a good example, many more can be found in those for network services)