Radorf It does matter. Next stage will be paired as follows: I ll take 1st place group 1 and pair it with 2nd g2, 3rd g3, 4th g4, 1st g5, 2nd g6, 3rd g7, 4th g8. And so on for other 3 groups. So every group has 2 winners, 2 2nd places etc.
So if you are 1st in your group you will have just 1 another winner from other group, while if you are 2nd you will play with 2 winners from other groups! Same logic goes for other places. If you are 4th you will have just 1 4th place from other groups.
So the higher you place the weaker your group is going to be. Little bit.π
Also important to note, that you will not face anyone from your current group in next stage.