As this article agrees, wiki's are indeed hot. I will summarize and add some of my own reasons whyevery organization should have and use one.
What is a wiki?
* a website
* anyone can add, remove, or otherwise edit all content, very quickly and easily
* term 'wiki wiki' is an ajective from the native language of Hawaii to denote something "quick" or "fast"
* facilitate internal team discussions
* maintain project documentation/FAQ
* reduce the amount of corporate e-mail
* single source of knowledge
* collaborative writing
* version controlled (easy reverts of changes)
* document changes are effective immediately to all viewing the wiki
* simple syntax
* support for tables, images, attachments, etc
I have been using MoinMoin, a wiki engine, for ~8 months and it has proved amazingly useful and changes the way we share information in the office place.