In some private emails to my friend Expat-leo (on my top 8 here), I expressed some of my frustration with the Wikipedia. In very blunt terms, I told Expat that, when a community tolerates unpleasant people, the community will attract unpleasant people and repel everyone else. Wikipedia has fallen in to this trap. Larry Sanger, one of the Wikipedia founders, expressed it well on Kuro5hin:

I stopped participating in Wikipedia when funding for my position ran out. That does not mean that I am merely mercenary; I might have continued to participate, were it not for a certain poisonous social or political atmosphere in the project.

There are many ways to explain this problem, and I will start with just one. Far too much credence and respect accorded to people who in other Internet contexts would be labelled "trolls." There is a certain mindset associated with unmoderated Usenet groups and mailing lists that infects the collectively-managed Wikipedia project: if you react strongly to trolling, that reflects poorly on you, not (necessarily) on the troll. If you attempt to take trolls to task or demand that something be done about constant disruption by trollish behavior, the other listmembers will cry "censorship," attack you, and even come to the defense of the troll. This drama has played out thousands of times over the years on unmoderated Internet groups, and since about the fall of 2001 on the unmoderated Wikipedia.

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A few of the project's participants can be, not to put a nice word on it, pretty nasty. And this is tolerated. So, for any person who can and wants to work politely with well-meaning, rational, reasonably well-informed people--which is to say, to be sure, most people working on Wikipedia--the constant fighting can be so off-putting as to drive them away from the project. This explains why I am gone; it also explains why many others, including some extremely knowledgeable and helpful people, have left the project.

Larry Sanger expressed far better than I could exactly what is wrong with the Wikipedia, what is wrong with Slashdot, and what was wrong with Usenet. This is one of the major reasons I left. Another one is that Wiki has certain political and religious viewpoints which are too strong to have as part of an Encyclopedia; people who try to be moderate are shouted down. See, for example this article (click on the "discussion" tab).

Wikipedia needs to fundamentally change before it can become a respectable encyclopedia. I do not think these changes will ever happen.