Wikipedia is a great resource and has proven to be reputable time and again.  However, as content is free for anyone to edit at any time, it is difficult to guarantee this integrity.  Any time I come across something that I need a quick reference for, Wikipedia is there for me to clear things up.  I use it, for personal use, as a reputable source.  When I am writing, I never cite Wikipedia, there are two main reasons for this:


1. This has typically been "banned" from an educational perspective. 
2. What you quote, may not be there later... 

They way that I do use Wikipedia for writing is simply as a reference.  It's great to get an understanding of a concept quickly. Also, there is a works cited section at the bottom.  This is wonderful, because it can give you ideas where to look for the information you need. 

When it comes to scholarly material:

Wikipedia is a good launch pad, but not a good place to land.