Somehow I added then deleted a post to the 23 things wiki because it showed up in the history. It seems like a great way to get input from everyone in a group. I created a simple wiki to use with the media specialists for gathering ideas for the meetings. I would have preferred it be private, but that was only available for 30 days, then I assume there was a fee.
The blog is one person who initiates the content periodically and others respond to it, whereas the wiki is intended for many to contribute content. A blog might be more appropriate for a teacher presenting content, but use a wiki when the intent is that each student is going to present an idea or topic.