Over the course of history there have been missed opportunities here or there to advance our collective knowledge. From incorrect assumptions to the instability of war to simple bad luck, we're clearly not as advanced as we could be.
What is the latest POD you can come up with that you think might have led to our advancement by 50 years or 100 years? So that by 1909 or 1959 we have the technology of 2009 with reasonable variation (clearly the exact technological package we have isn't going to be the same at a given point in time, with a given POD.)
For example, I would guess that a continuing, flourishing Roman Empire might lead to a world at least 50-100 years ahead of us, if not more. Can anyone think of later POD's?