I don't know why this is being down voted. The first sentence is absolutely true. We don't even have a general outline of a theoretical approach to designing a general purpose intelligence, let alone implementing one. Until we do, any speculation about a time horizon for implementation is a pure guess. How are those guesses working out so far?
1960s Herbert Simmons predicts "Machines will be capable, within 20 years, of doing any work a man can do."
1993 - Vernor Vinge predicts super-intelligent AIs 'within 30 years'.
2011 ray Kurzweil predicts the singularity (enabled by super-intelligent AIs) will occur by 2045, 34 years after the prediction was made.
So the distance into the future before we achieve strong AI and hence the singularity is, according to it's most optimistic proponents, receding by more than 1 year per year. So I predict that when we get to 2045 strong AI will be on the slate to be achieved by about 2090.
edit - I am not in any way denying the achievability of strong AI. I do believe it will happen. I just don't think we currently have any idea how or when.