I spent a couple of hours playing with PBWiki.
It promised to be simple to use, and I have to agree - it took very little effort to become familiar with the set up.
Click on the image below to link to the pages I created while exploring PBWiki.

First impressions, without having yet used it with students, is that it has a lot of potential in its use.
One of the key considerations before using a Wiki with students is introducing the culture of collaboration and the purposes behind using the Wiki. Simply providing the tools for students to collaborate doesn’t ensure that the collaboration is fruitful.
In class exercises on collaborative writing could be supportive in using an online collaboration tool. As with all of the tools and ideas with Web 2.0 they need to be introduced in a way that support realising their benefits. Lack of planning and support will quickly highlight that simply using web 2.0 tools does not in itself produce exciting learning activities.
Tecahers in using wikis need to emphasis the product and outcomes of using the technology, not the technology in itself. Wikis are not used to collaborate, they are used to collaborate to produce something - and it is the something that is of value, not that it is a wiki.