Interesting piece of research here:
However, the trend is clearly downwards. Fitting a power law give a slope of -0.68. This is scary. Three raised to the power of -0.68 is 0.47. This means that when you triple the number of employees, you halve their productivity. Or: When you add 10% employees the productivity of each drops by 6.3%. Of course, since 3 times half is greater than one, your total profits are typically growing.
There are a huge number of startups, young and old, famous and unknown, small and big, building collaboration tools out there. Even Google had a crack at it (such a shame they chickened out). They are all, effectively, trying to solve this huge problem.
If anyone does manage to solve this huge issue conclusively, there is a lot of money to be made.