I agree, the concern over 'idea-theft' shouldn't be a real issue. If it is, I find it unlikely that the person with the idea will end up executing it anyway.
The way I think about it is that if the idea is so good then you should rather go implement it. There are many advantages here. First, by implementing you can validate a lot of assumptions you made. Second you got some experience in the area and likely know a bit more and your idea is more refined.
Because what's worse than someone stealing your idea: to see someone who had a similar idea as yours and they have already implemented it. It happened to me a couple of times and since then I just start thinking about how I am going to execute on my idea the moment I feel striongly about something.
Its really nice to see so many people agreeing on putting your idea out there. I am in the process of building a web portal (http://friendvestment.com) that allows people to share their ideas/startups looking for financial/technical partners. While building, one of my main fears was that most of the new people will worry about sharing their "big" idea and ask for security, etc for their ideas. But the fact that an idea has zero value if it is just an idea, seems to be resonating a lot these days through people...
Because what's worse than someone stealing your idea: to see someone who had a similar idea as yours and they have already implemented it. It happened to me a couple of times and since then I just start thinking about how I am going to execute on my idea the moment I feel striongly about something.