There's a lot of science blog activity debating the utility of Wikipedia (e.g. Eye on DNA, Wired Science, Science Roll, Epidemix), and I've never been one to not jump on a good bandwagon. In general, I think the various viewpoints agree more than they disagree, but there is a significant divergence of opinion on whether Wikipedia can be saved from itself. I will boldly and decisively plant my flag in the mushy middle.
I find Wikipedia very useful as a general reference (and often link to it from here), but it is clearly flawed. The anonymous nature has always given me the willies. In general, I have found the information pretty good, but often maddening. For example, I was looking up a particular branch of Protestantism today (in the interest of general knowledge), and unfortunately the entry was written by a true believer (and not flagged) -- surprising, since usually WP bends over backwards to flag everything not written in a neutral style. A friend once asked me for some help for her daughter's high school project on serotonin, and I was surprised to find the Wikipedia entry lacked any history of its discovery (but did I edit it then -- no! -- however, it does look like its gained a little bit on the history). Some Wikipedia entries have absurd levels of depth, whereas others are too shallow.
Back in grade school the library always had multiple encyclopedias, which often had different strengths and levels of detail. At home we had both Junior Brittanica and Encyclopedia Brittanica, though both purchased before my entry into this world. I quickly learned that my then favorite topic was badly truncated, with the big one ending during the early Mercury shots and the Junior set going into Gemini (I think). Wikipedia is amazingly up-to-date, with events showing up there before the newspaper with the same info can hit the street. But in any case, the world is probably best served by competing encyclopedias.
An alternative to Wikipedia has been launched called Citizendium, and the model has some interesting differences from Wikipedia. Contributors will be non-anonymous and a much more limited in number, and generally chosen for recognized authority. Alas, Citzendium is pretty limited in coverage. Looking at my last post, things are pretty bad. 'Ailuropoda' brings up nothing, whereas the first hit for 'panda' is to an article on creationism (those poor hypercute ursids, commandeered for pseudoscience!). 'Dodder' brings up articles on horizontal gene transfer. Wikipedia's article on serotonin is flawed, but Citizendium's is non-existent, though there are articles on neurotransmitters and Julius Axelrod. Even more striking, 'Watson-Crick' pulls up nada. Yikes!
What is potentially interesting is that Wikipedia is on a 'copyleft' model, which theoretically means Citizendium could (and plans to) use Wikipedia as a major building block for their effort. So, it is possible that Citizendium will evolve to largely be a buffered version of Wikipedia, slower to be updated and smaller in scope, but with the worst excesses filtered out. Of course, the copyleft also means Wikipedia can raid Citizendium for the improvements. Let's hope this works out to a virtuous cycle.
For the sake of completeness I feel I must include the other heavily publicized encyclopedia effort, but I can't recommend it. Conservapedia is an explicitly ideological view of the world. In particular, it attempts to be even-handed towards various branches of creationism. So the article on the speed of light (at this time of writing) touches on the 'minor' problems it creates for young earth creationism and cites only a creationist tract, but doesn't discuss at all Michaelson-Morley. We learn that kangaroos originated in the Middle East. Now, if you dig you can find that some folks who like the general concept but not the anti-science are trying to contribute
Wikipedia is flawed, but what to do? The eager can try to reform Wikipedia or lead the expansion of Citizendium. But if Don Quixote is your hero, then perhaps you'll try to keep Conservapedia on the straight-and-narrow.