How do I enable Wiki-style markup?

Wiki-style markup is not enabled by default (Plone 3.0) -- to enable it, go to the Plone Control Panel (via the Site Setup link) and click on Markup. From there you can configure "Wiki behavior" by selecting from the three possible content types (Pages, News Items and Events).

Note: "Wiki links" are triggered by enclosing text with double parenthesis, e.g:

Visit my ((new page)) for more information.