[Lazare]

I think this needs to be pointed out and stressed, especially since it's applicable to way more than just computer games:

Nothing makes your customers as upset as the feeling of broken promises. Don't promise what you can't deliver.

[SkyMarshal]

Interesting problem. Everyone knows that intuitively, but people do it anyway.

Instead, how about: Don't promise any specifics until you've already implemented them, and all that remains is debugging and optimizing.