Whenever I am looking at a Wikipedia article for research purposes I:
1) Check to see if for the particular information I write down there is a source citation. I write that citation down so I can look that up later. Citations are heavily encouraged at Wikipedia, and an article that doesn't have them usually has a warning message on it at the top stating that the article lacks citations. (e.g. unfortunately, the entry on Genealogy) Particular facts within the article can also be labeled as needing a citation.
2) I look at the "History" of the article to see how old it is, and what the more recent changes have been. If it is a relatively new article, that decreases its reliability in my mind. The more people who have read it, and made changes to it, the more accurate it is likely to be. If it is a very new article, I may click on the names of the editors to look at their user profiles and see if they claim any expertise.
Due to recent controversies in this area,
I also check the most recent edits to see if any of them impact the information I am interested in.
3) I look at the "Discussion" page to see if there have been any disputes over the content of the page.
Yes, this is more work. But these added steps do help one judge whether a particular article is reliable, and it is still quicker than going to the library. And if there is a source citation, I can take that to the library, and save a lot of time I would have spent there trying to find the information.
What people have to realize is that the editorial process that goes on at print encyclopedias goes on at Wikipedia too - it just happens live. There's no way to know at what point in the process the article is unless you check the history and the discussion page. Like many tools - Wikipedia is neither inherently bad or good – it depends upon how you use it
The above is edited slightly from a post I made recently to the APG-L list. I am not a professional genealogist, but I do subscribe to the list to hear the discussions of professional genealogists, and I occasionally contribute to the conversation when I think I have something of value to contribute. The subject of Wikipedia was raised, and I have had experience editing entries on the site, and I am a SysOp on a local St. Louis wiki.
Part II will focus on advice for the individual who wishes to edit an article. Anyone can.