There is a great account of Maxis Senior Development Director Eric Todd's talk at the GDC on Gamasutra about pre-production through prototyping, which is a very important question in game design: what can game designers learn from prototypes? how early in the development of a game could they use them?

The talk was about pre-production. Some excerpts:

a prototype is used to convince others that your concept is "worth the risk of a full production".

Todd explained that the benefit of having a working mechanical model at hand is that, as far as communicating about design concepts is concerned, "words are fundementally a terrible way of communicating interactivity." (...) Demonstrating the concept, Todd showed a utility that allowed an amorphous worm creature to be prodded, deformed, and manipulated – he demonstrated how it felt to mess around with the utility, which seemed pretty tactile. As Todd said, having a tool like this "short-circuits" an inane conversation (...) prototypes should be as focused as possible upon just the few things you need to demonstrate to someone; (...) when someone finally threw together a prototype to show off the battle system and its animation style, he hot-wired the utility with PlayStation controllers and unveiled it during a staff meeting so as to delight the team and get them fired up about the project. Of course, there was no practical need for the Dual Shocks; there are no plans to place Spore on any console, and anyway users aren't really meant to interact with the game that way. That didn't matter; turning the battle system into a free-for-all brawl created energy. It led to people feeling more ownership over the project and to have more fun with it. The prototype also effectively educated the team what that game component was like, giving them a further impression for the way the game as a whole might come together.

An example of a prototype from the game Spore: Why do I blog this? these elements are very interesting and have a wider impact than just video game design. It made me think of the discussion we had at the Crystalpunk workshop about tools and architecture.