I've found some errors, pretty subtle ones too (check out the definition of natural selection. . . that's how people perceive it to work, but it's not quite right as stated; it also differs from 19 of 20 definitions returned by a google definition search, and that given in a textbook on evolution), but yeah, I think on the whole it's fairly reliable. I notice the mesoamerican archaeology/anthropology pages are particularly well done, apparently by an effort to coordinate work on that section. I think it's things like this, truly interested people working together to build a resource, that make it more reliable that many other internet resources (particularly those written by a single person with poor or incomplete understanding of the topic).
Obviously if you're doing serious research it should only be a starting point, just like any other encyclopedia -- I tend to use it to find terms I didn't already know, or interesting facts to verify -- but for a casual user the errors aren't a big deal.
And because of the nature of Wikipedia there are a lot of topics that wouldn't be covered by most normal encyclopedic resources (popular culture, for example). I couldn't care less about these things most of the time, but it's nice to have a place where the uninitiated can actually find information (web searches suck if you don't have a clue
![bluetongue.gif](http://www.cspacezone.com/forums/public/style_emoticons/default/bluetongue.gif)
).