Another thing I see a lot in different forums, is asking the wrong people. A good example of this, is an open review of a web site. I've seen this on a many different forums, not just WA. Here is an example.

Question:Will someone give me a review of my site http://www.somewebsiteurlgoeshere.com

While an open review is a great thing, and I encourage people to do it. Maybe if your idea is only half done, you should seek a more selective audience. Here at WA we have the wonderful networking tool, WA spaces. So instead of posting it to a forum, you could ask some friends from WA spaces and try and get a one on one approach rather than drive by comments.

For forums outside WA, try and keep a look out for the people on top of things and consider PM(private messaging) them, and getting there insight.

This also helps stop the dreaded, "Man I have this really great idea / niche, I tossed it together and haven't really worked a ton on it, but what is everyone thoughts?" While the rare evil guy in the corner, snatches up the idea and runs with it all night. By the time you have your site polished, you already have competition. Whereas if you asked your group of friends, there is even less chance it will be leaked until you have it polished gold. At that point even if someone else takes up the idea, you already rule the market.