Diminishing ability to contribute
Fragment of a discussion from Talk:March 2011 Update
On popular culture topics, it may be true that the average Wikipedia article is good. On the majority of academic topics however, you are better off picking a random source from the en.wp article's references and reading that instead, or searching google books and finding a suitable book for larger topics. Wikipedia's strength is quantity (of articles) over quality (of any given article) by and large. There was an academic study on the quality of FA-rated articles; about half of them were found deficient by experts. Yes, Wikipedia is better than Britannica, but nowhere near a specialized source for any given topic, or even broad area (say like the Stanford Encyclopedia of Philosophy).