The answer that Wiki proponents use is: "It's just as easy to fix as it is to break, so it won't stay broken for long. Instead of going to an online forum and complaining about it, you should have fixed the page."
Most Wikis will preserve older revisions of the page. If you cite it in some kind of article or academic paper, make sure you also include the revision of the Wiki page you used.
On top of that, it's probably a good idea to save a copy of the page (print to PDF works well for this). You can't be sure just how many old revisions of pages the Wiki will remember.
Another big concern for Wiki's is the "opinionated" information that makes it into the Wiki. With non-technical subjects in Wikipedia (especially political ones), you'll find a certain level of "bias" in the articles.
It doesn't mean that Wikipedia is completely untrustable. It just means you have to use some judgement when reading it.
That said, I've been having a lot of success with a Wiki on our internal company network for maintaining documentation.
