I'm not afraid to post ideas anymore, because of a post I read on Micechat.
Nautilus on MiceChat once had a very good post about posting ideas on messageboards:
Who's gonna take it? Really? That's what cracks me up about some people on this board, being protective and secretive with their ideas because they want to use them "when they get to WDI". Don't be silly. It's not a big deal to post them on the internet, I have yet to see ANY ideas posted around here get fully realized in the parks. I wouldn't be that worried about someone taking my ideas; it would be quite obvious that if they did steal something, you back it up with the original source. Chances are slim anybody here gets into WDI, and chances are even slimmer that you get to implement your ideas and have them come to full fruition; you're gonna get assigned to someone else's project. But the ideas you have now, if you fully develop them with concept art and good documentation can make good portfolio pieces.