The problem with using wikis with classes so that they can learn about new material are the ground rules for the wiki. If you have your own wiki set-up for the class or the class share a private wiki then you can set your own ground rules.
This is not the case with deciding as a class exercise that you will write a wikipedia article. Wikipedia requires that articles are not essays, that they are not original work and that they are objective. This is a very difficult standard to meet as a learning objective, and one that is likely to result in students performing the task taking a surface approach. If you follow these guidelines then there is no possibility of comment or true synthesis. It encourages those making entries to cut and paste.
One of the great advantages of knowledge is what you add to it as it goes through your hands. A list of web-links is not very useful. It becomes useful when it is annotated and rated. This is when it can be evaluated and when it develops as knowledge.