They make it sounds like this confirms the old saying, when really it's just the opposite: The saying says that any two people are connected by a chain no more than 6 links long, while this study says 6.6 links is the average, with some chains as long as 29 links.

Also there are serious selection problems with this study, since it's only dealing with internet-savvy people living in economically well-off, internet-connected countries.

Still it's interesting that someone is at least looking at this pool of data, and I would be really curious to find out if the number would be similar for data sets from other instant messaging services.

The data is definitely incomplete.... Though you could argue that the average has to be significantly less than 6.6 at least among this population since msm messanger is only one means of connection. If for example those who are 29 links away through msn are are only 8 links separated through another medium than the outlier of 29 would have to thrown out and replaced with 8.

But as you mentioned there is a serious problem with the selected population (i.e. people who have the means and knowledge to use instant messaging.)