I love Wikipedia. It's the original site that works because of the constraints it imposes. You have to follow the spelling and grammar. You have to format it this way. You have to use the objective voice. All the pages are going to look this way. Jack Dorsey mentions this same idea in the context of Twitter: its strength is the 140-character limit. The great thing about the constraint in the case of Twitter is that it guarantees you'll be able to read something quickly. And in the case of Wikipedia you can consume the information very efficiently because you know what to expect and your brain isn't trying to wrap itself around other fonts or formats.
Another way I look at Wikipedia is that it's partly a group of people that read the news and then turn it into history. Last week, Gabby Giffords and 18 or 19 other people were shot. Afterwards, a series of news stories about what happened came out, each one filling in more and more details, but then the next day's news comes out and that story falls out of the public eye. Wikipedia reattaches those bits of news not just to a date and time but to the relevant actors in history.
The community also does a good job of carving out the boundaries of what's notable so that the set of stays manageable. My interpretation is that the collective subconsciously chooses not to allow stuff that it can't take responsibility for maintaining.