I recommend this plugin. My own favorite use is with $:/tags/AboveStory — so the pinboard floats above the rest of my wiki.
(My use case is colorful and personalized dynamic reminders to students — which they can “dismiss” my clicking the pins, but which re-appear on reload.)
Are the wiki’s read-only? If they should re-appear, that’s OK. But for read only wikis you could use the browser storage plugin and only “store” the “dismissed-state”
Right, this is an important option, and I may experiment later with allowing students to set certain preferences (such as palette, perhaps, and favorites) via browser storage. For the pinboard purpose, though, I want the visibility reset on each load, since the pinboard includes announcement-like content that I tinker with often.