Paul at the Product Beautiful blog hits the nail on the head:
First, develop to your average user, not your subject matter experts. SME’s will feature pack your product with interesting features of dubious usefulness to the rest of the Market. Worse, they will mutate core features (armor and firepower) to the extreme, and you’ll end up with a scenario where you have important features that should solve user’s problems but are so bloated that they are unrecognizable or hard-to-use (Macros in MS Word, Adobe Download Manager, the HTML blink tag, etc). BTW, Engineering/Development are super-SME’s, so don’t let them define the product - ever!SMEs are a valuable resource, but the primary source of requirements should be buyers and end users, as I have mentioned.