When using a wiki with a customer or client for the first time, check to see if they understand what it is and are open to using it. Using a Wiki and getting acquainted with its underlying philosophy might cause difficulties for “conservative” customers.
Customers might not be willing or able to use the Wiki. An indicator of problems is when a customer does not visit the wiki to review links sent around. If this happens, check with them as soon as you notice that they aren't editing or commenting on wiki pages that pertain to them.
Clarify experience with Wiki when new customers join the project. If needed, show some customers how to use the Wiki or determine a team member to act as customer proxy. Clarify how reviews are done (e.g., by showing how to edit a Wiki page). Ask customers to set up their user homepage and provide a sandbox inside the Wiki.