Empirical tests are important. In fact, I would probably alter the publicly-visible workings of the site to get better data that can help us discriminate between the competing hypotheses about how LW continues to have the high s/n ratio it does have and about how to protect it from various stresses (like discussion of mind-killers). The online rationality quiz hosted by darius at http://wry.me:7002/ is an example of the kind of thing I would add to the site.

As to my hypothesis that growing the membership too quickly risks LW becoming just another online community, that can be tested without altering the public face of LW: in particular, it can be tested by collecting statistics on the rate of the appearance of new commentators, posters and voters and by comparing that to the rate at which established voters stop voting.

I will admit that I stopped voting about 6 weeks ago in response to the increase in bad comments probably caused by influx of new participants from the Harry Potter fanfic and the (simultaneous with the fanfic) efforts by one of the SIAI visiting fellows to apply SEO techniques to the site. I am by disposition easily annoyed, and when I exercise my "critical / judgmental" mental state enough, I tend to get caught up in that state and cannot get myself out of it, which bad for my health and for my personal relationships, and it was just too annoying and too internally costly to pay enough attention to comments by new writers and the usual old writers of poor-quality comments to vote on them. So, you see, I already have one piece of empirical evidence (namely my observation of my own behavior) that LW is more stressed than it was 6 months ago, and consequently now is not the time to add a new stressor.

The only way I know of for LW to continue to have a positive effect on the world is for it to keep the quality of its conversation high. (Of course, the benefits it already has had on the world, e.g., in the form of increasing the rationality of readers, can compound themselves, e.g., by the more rational readers and former readers doing good in the world outside LW. But that would happen even if LW disappeared today.)

jimrandomh has identified a very potent way to improve the world: try to apply whatever processes make LW as good as it is to a greater fraction of the public discourse.

The strongest argument I know of against jimrandomh's proposal is that it does not talk about why he thinks LW came to have the high s/r ratio it does have and how and under what conditions that quality is likely to be lost.