I'm not sure how alarmed I am by this. I certainly have seen this in action on Wikipedia at least, if not on the scale described, but I have little doubt it occurs and I can think of a couple events whose online conversations show evidence of this sort of manipulation.

To some degree I admit, when I see the overwhelming online conversation swaying in one direction, it does influence. On the other hand, partially because I know online conversation manipulation is out there, I become less prone to read comments. I used to always read comments to Economist articles for example, now I rarely do.

Ultimately, if there is online conversation manipulation but people barely pay attention to it, it will be overwhelmed by all the other random sources of influence in our lives. Whether, traffic, etc. all play some influence on our opinions, if the impact of the online conversation manipulation is less than that, I am not alarmed.

There are two other aspects of this worth thinking about:

1. What is the problem we have with online conversation manipulation? Is it the sock-puppets alone? If you replace sock-puppets with volunteers, is that different enough? If you take volunteers who otherwise wouldn't participate in that online conversation, is that different enough? What are the aspects of this that are different from a legitimate campaign to change the opinions of others about a position you think is profoundly wrong.

2. One sad aspect of this is that it dilutes the impact of anonymous or semi-anonymous voices on the web. This was a short-cut to influence for ordinary web users. On the other hand, this is in a way natural, whenever the impact of a medium becomes popularly recognized, more people will try to utilize that medium, and its impact will be diluted. In the same way, just having a website used to be a short-cut to influence, but now has little effect.