Many questions get asked again and again. Why? Because people are not searching for previous answers before asking questions.
Stackoverflow suggests some similar questions that have already been asked when people are typing in their questions. It's therefore easy for them to see that the questions already exist.
This system also relies on good questions being voted up, so they appear at the top of the list. I have asked several (dare I say) well-worded questions (and usually answered them well too), with a view to providing a resource for people to refer to. This effort is wasted by the questions and answers receiving no votes, and the fact that people never search for them anyway.
So, TMW please implement question suggestions like Stackoverflow, and regular users please vote for well-worded questions.