The division of Korea and the assignment of Vietnam to France were certainly not very good in the long run. These were just two portions of the almost inane way that the world was divided by the victors after the war.
If you look at Africa, the Middle East, Asia, etc., the divisions were made along arbitrary lines rather than ethnice or historical ones and have led to immense amounts of conflict in many if not all of those regions.
You could point to the incredibly terrible condition of North Korea even today and the hardships that have been visited upon the population there simply because of an arbitrary division of the country.
The major negative effect I can think of is that it led to the Cold War. It did this, you can say, by letting the Soviet Union have all of Eastern Europe. This was bad for us and bad for the people of Eastern Europe.
Another one is that it split Korea into two countries. This helped lead to the Korean War and it has led to the problems that are going on right now between North and South Korea.
Finally, you could say that it led to the Vietnam War by letting France have Vietnam back after the war.