Other useful books/info: The Pragmatic Programmer has very useful advice regarding planning and estimating. And planning is a central part of the whole extreme programming philosophy (don't call it a methodology!).

Personally, I tend to do sufficient planning until I start making broad generalizations, then code up to that "point", go back to planning, then iterate iterate iterate. The time for this initial period depends on the scope of the project -- it could be 15 minutes or it could be a week or two.

Chris
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