In my spare time I have been coding a MediaWiki extension to generate quizzes automatically from Wikipedia content.
I would be *very* interested in your feedback, so I have put a basic prototype online, available at http://wikilearner.net/wiki
It's rough on the edges, but I hope you get the basic idea.
To be quizzed on content of your choice, simple create a new article on the wiki, copy-pasting your favorite Wikipedia content. I suggest you remove <ref> tags, templates, and alike which are not yet supported on my wiki.
Cheers, Justin