The Half-Life of Code

I've been thinking about the half-life of code.

In his Software that Fits in Your Head talk, Dan North defines the
half-life of software as (I'm paraphrasing) "the amount of time required
for half of an application's code to change so much that it becomes
unrecognizable."

In that talk he tells the story of working on a high quality, non-trivial
application whose code's half-life was six weeks.

Yup. Six. Weeks.