Just came across a great term on Tim Bray's ongoing site: Development by Accretion. He used it as a throw-away comment when talking about something else, but it struck a chord.
From Tim's posting:
I ended up having to write some real dodgy ad-hoc code to discard the right-side apparatus in certain poorly-thought-through special cases. Hmm... I don't want to write a bloody soup-to-nuts editorial system by accretion, but the slope is feeling slippery.
Unfortunately, this model of development will tend to happen on projects that are under time or resource constraints (and what project isn't?). CAREO is guilty of this, which explains the refactoring post yesterday. Ideally, we'd stop active development for a month or so, break the code into better-organized nuggets of goodness, and document the works. That would at least mitigate the nightmare of accumulated accretion.