It's doubtful that any good will come from attempting to establish guidelines for what is and isn't fair play. There's a couple major problems with the idea that I can pull right out of my, uhm, head.
1. Logistical Issues: Due to the "work in progress" nature of DF, the game fundamentals will continue to change, sometimes radically, from month to month. Any guidelines that we establish will need to be re-worked constantly. Something that was/wasn't cheaty in 2D DF would be a different story in the early days of the Z-axis and yet another different story today, and again next month. Maybe after DF 1.0 comes out in 2011 or whatever there could be an "according to Hoyle" discussion, but it seems unworkable until then. Also, what governing body will maintain the rules? Toady? A mob on the forum, armed with polls? Whoever happens to be posting the most this week? Batman?*
2. Philosophical Issues: Cui bono? What's the benefit of having any consensus on these issues? Consensus is a vice as often as it's a virtue. Attempting to establish a baseline for fair play would be ignored by most people, and likely devolve into an endless, fruitless cycle of flames, trolls, and circle jerks among those that do.
The notion of establishing orthodoxy isn't without merit, and I'm not arguing against social cohesion in general... but one cannot frost a cake before it has left the oven. One the game is more-or-less complete you should start this thread up again, and I look forward to tossing my curmudgeonly old self into the mix. For now, this just seems to be opinion gathering-- and that's interesting enough in itself, but there's just nowhere else to go with it.
*(The correct answer is "Batman," but sadly the only hero that even occasionally plays DF is Ironman, so we're SOL here.)