The guys over at GameSpy have posted up an article discussing the design and writing aspects of Portal at GDC 2008. Take a look:
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"Even though it was among the very last panels at this year's GDC, the Portal post-mortem was undoubtedly one of the most highly attended panels of the show. In an enormous ballroom packed wall to wall with absolutely zero standing room available, Writer Erik Wolpaw and Team Lead/Level Designer Kim Swift expounded upon the topic of integrating narrative into game design... more specifically, Portal's game design."
Be sure to see the rest here.