They play fine on tray loaded drives, not sure about the superdrive though. Check this site for lots of great info, and maybe the answer to your question: http://www.minidisc.org/minidisc_faq.html
The FAQ at minidisc.org relates to Sony's MD, you know the MD discs with a plastic case with the disc inside it.
For the 'mini CD', Apple's official respose to this question is no. Only the full-size optical discs should be put in a slot-loading drive. The 3.5" mini CD will work on tray-loading drives as Natobasso says, but they won't work in the slot-loading ones. See Apple's full article : http://docs.info.apple.com/article.html?artnum=58641