Conversely, one might argue that the type of gamer who posts on forums is potentially engaging with the material in a way that is more useful to game designers than the way a more casual gamer does. A forumite is, possibly, someone inclined to analyze the game, test it to breaking, and - if they're not enjoying something - provide a reasonable explanation as to what it is that isn't working.
Potentially.
Which is not to say that every whim and gripe of forum posters should carry equal weight, nor that forums should be the primary guiding force for design changes or the direction of development. Only that, at their best, they can be a source for thoughtful feedback that probably won't come from anywhere else.
Far better, I would say, that designers probably shouldn't give forum feedback any more weight than it merits - whatever that means. But I also suspect most game designers are likely smart enough to know that already.
(In writing workshops, one of the evergreen pieces of advice is that if more than one person tells you some section doesn't work, you should pay attention - but you shouldn't pay much heed to what anyone in particular advises you to do to fix it. I think there's a similar dynamic going on in game design and the type of things that get discussed on forums.)
