this was a rather long-winded post to ultimately plug a project you created. also, I feel like we get one of these a month, it would be helpful if the post explained why this one is better than any of the existing and/or failed attempts to do something like this.
Also, for some real advice, the reason these sites generally do not take off is despite the chorus of "ideas don't matter", people don't really believe that when they have what they think is a good idea. If someone has what they think is a million dollar idea they are apt to keep quiet and not want to tell anyone about it publically like this, and reveal it only insofar as it provides tangible benefits to them. Customer Development does not mean shouting your idea from the rooftops, anyway. There's a gradient between "I will tell you nothing unless you sign an NDA" and "I will post my idea to the public on the internet complete with a full explanation as to why it will work."
I agree that there is a gradient and I can tell you that if someone wants you to sign an NDA then WTF won't really help them but for everyone else, getting feedback as early in the lifecycle as possible is worth a lot: It could save you a lot of time and money.
We designed WTF for ourselves in a way. We wanted somewhere we could test out an idea before committing too much time and resource to it. Somewhere we could show-off our idea, get feedback, change it accordingly and then re-show it and so on.
WTF is a guide; It will not be 100% accurate but it might just stop you from wasting months of your life on something you thought people wanted.
The other side of that coin is that you may find that your "Facebook Killer" application isn't a total flop: There may be something you could salvage from it, maybe a particular set of features, and that is what WTF is designed to help with.
Example: I'm working on an PDF replacement to support marketing automation. The people looking at this website may or may not be my target audience. Thus, the feedback may or may not be useful.
You are right in that not everyone that comes to the site will be representative of your audience but "outsiders" can have their own insight into something that you may not have considered.
All the mechanisms we will be putting in place (comments, voting, project questions etc.) are designed to help you decide if your project is worth pursuing: They will not be 100% effective but they will be much more effective that creating your project in total isolation with no feedback from anyone.
These mechanisms will evolve over time, for example, we may find that straight up comments may be useless but a scoring system, where other commenters can vote some up or down, could provide far more value...
WTF is still evolving.
It is very easy for people to have bad experiences, decide that they know what went wrong, then proceed to act on those theories. However hindsight is not 20/20, it is just speculation in the absence of being able to be proven wrong.
Therefore until you've either had feedback from people you trust, or have a success under your belt, it is wise to temper all "lessons learned" with the provisional, "I suspect" and the emphatic "I was wrong before, and may be again." This is difficult, but it is only when we keep track not just of what we think we know, but how certain we are that we know it, that we truly put ourselves in a position to actually learn from experience.
Now feedback on the new platform, WTF. Any site which seeks to offer users feedback from other users, needs to do some careful thinking about how you're going to attract people who are worth getting feedback from. Else you won't attract a pool of people giving feedback who are worth listening to. That is why Ask HN can work - there are a lot of people already here who can offer good feedback and sometimes do. But they are not here because they want to offer that feedback 24/7. And if this site became nothing but Ask HN, then they wouldn't stay.
I can't tell you how to get the people you want involved. You'll need to form your own theory. I believe there are multiple possible successful strategies. I also can't tell you how to monetize it. From what I've seen discussion forums tend to be popular but don't monetize that well. (Though if the feedback you get allows you to launch a successful parallel startup, maybe that is good enough for you?) However if you aren't constantly trying/testing your own theories around those central questions, I guarantee that you'll not find workable answers.
And some feedback to willthisfly.net:
For it to have a chance to fly it need (more obvious) incentives for people to comment. Something along the lines of having to comment on three projects before you can submit your own perhaps?
