So Wikis seem to be a lot like Google Docs. I guess that the difference is that anyone on the web can view your wiki and only those invited can view google doc?
I like the idea of using Wikis for book reviews! My kids toyed with online book reviews through Scholastic last year, but this allows for more freedom!
I also think you could use a wiki as a fun way to solve a mystery or scavenger hunt, of sorts!