Talk about a key word on the Web 2.0. I have made so many wikis in the past 9 months it is crazy. I will say at first they scared me to death. I understood blogs and what they represent, but the wiki sites seemed confusing to me.
I will say that not all wiki sites are created the same and each are unique in the resource they offer. Below I have two of the sites that I have used and the pros and cons behind each:
http://www.wikispaces.com: Pros: Free with no advertising if used for educational purposes, a discussion feature that can be used to make sure that people are collaborating. Cons: No spell check and has issues with formatting at times.
http://www.pbworks.com: Pro: Free with no advertising, spell check and formatting relatively easy. Con: No discussion, side bars can be tricky to format.
Overall, my experience with wikis has been a positive one and I look forward to more projects in the future!