Because it’s collaborative, errors are found pretty quickly. Some pages are locked during certain times to prevent vandalism, etc. Also note any “[citation needed]” remarks on the pages you view, as most definitive statements automatically require that references be made as one would see in published papers and books. As with any source, it would behoove the reader to follow up on references if their research is important.

More info on that here:
http://en.wikipedia.org/wiki/Reliability_of_Wikipedia

I did wish to comment that, as you stated, WIKI has user contributed content. It is not referred – and as such is prone to errors. It is a fast, general source of info, but shouldn’t be used to base decisions, etc.

Thanks for the great TIPS!