Well, a tease of it anyway.
Gamasutra have posted a little of a Portal post-mortem, written by RPS-crushes Kim Swift, Erik Wolpaw and Jeep Barnett. It’s taken from the January Issue of Game Developer, which can actually be bought in a PDF format for (er) money. Man, I wish people would give us money. Anyway, the two quoted sections involve the development of the game’s fiction and overcoming the technical stuff. Since I’m feigning ignorance of tech-stuff, let’s quote from the origins of GladOS bit. That sounds like an RPSy thing to do.
“Before the writing started, we met with Erik and discussed our list of narrative constraints. Since at the time we were using some Half-Life art assets, and because we wanted to leave ourselves the option of someday using the portal gun in a Half-Life game, we decided that the story should in some way connect to the Half-Life universe.