It is literally the largest collection of human knowledge ever assembled.

I think that's called Google. And one of the big weaknesses of Wikipedia, at least in English[0], is that few Wikipedia editors go beyond Google or their own personal experience in sourcing articles. There is a huge amount of well curated information that still exists only in research libraries. Even though Google has made efforts to digitize that information, various technical and legal barriers make it hard to make that information generally available, and anyway most Wikipedia editors don't look up most of that information.

[0]The problem that Wikipedia has in many other languages (but less so in German than in most languages) is that the articles are mostly cribbed from the English articles, and the English articles are not very well sourced. I read several other languages, and two others besides English well enough to use those languages for professional research, and I often trace Wikipedia interwiki links to see what articles in other languages say about the subject I have researched most thoroughly over the last two decades. The English version of Wikipedia tends to set the tone and provide most of the references for many other language versions of Wikipedia.

Another problem that Wikipedia has, as Wikipedia reports, is an "unsustainable" decline in the number of administrators willing to help the project actively.

http://strategy.wikimedia.org/wiki/Story_of_Wikimedia_Editor...

The Wikimedia Foundation points out that if the number of articles grows while the number of administrators shrinks, it will be very hard for Wikipedia to meet the foundation's stated goal of improving article quality.

All of the above being said, I am a Wikipedian because I thought the original vision of Wikipedia made sense, and I have liked using Wikipedia as a reference resource from time to time. But in my efforts to volunteer to the project and give back to the editing community, I have discovered the problems I just mentioned above. Those problems need to be fixed for Wikipedia truly to rise to world heritage status.

After edit: I might as well edit here, after taking a look at the other comments. Maybe my point of view is old-fashioned, having been educated for two postsecondary degrees at a large research university, but to date, for sure, any large university library has much more total information inside than ALL of Wikipedia, in all languages combined. (One quick way to verify this would be to do something that German Wikipedia has attempted to do, namely to make its complete content available to a print publisher.) Wikipedia as a whole still contains a lot less information, and rather more poorly curated information, than any research university's library. So if there is a claim just on the basis of aggregate information collection size for regarding Wikipedia as a world heritage site, there is a much stronger claim for that for any well administered university library.

One thing each of you can do to get a reality check on Wikipedia is to look up several articles on some subject that you know very well, a subject that you have taken care to research thoroughly in other sources, and see how long it takes to find something to fix in the Wikipedia articles. That Wikipedia is an online resource "anyone can edit" was a bold social experiment, and it has proven to be a largely successful experiment, but when I want do serious research on any subject related to my occupation or to my family's health or well-being, I still turn to sources beyond Wikipedia, because Wikipedia today is nowhere near inclusive enough of the best information in the world to be relied on without double-checking other sources.

P.P.S. Last edit to this post (I think): Wikipedia is user-editable over long time spans, as several commenters here have mentioned. HN threads are not as long-lasting, and each post has a short edit window. Does anyone have any reliable sources

http://en.wikipedia.org/wiki/Wikipedia:RS

that suggest that any of the factual statements I have made in this post are untrue? What sources do you have about the information content of

a) Google,

b) a typical research library,

or

c) Wikipedia as a whole as of today?