Recently I upgraded my Knowledge Base from using Mediawiki to Atlassian's Confluence to enhance it's functionality from a plain text based wiki to a fully customizable environment that indexes everything that you input into it. Being wiki pages or even attachments in many forms like .doc, .xls, pdf, etc.
A Knowledge Base can be a great source of information for a company. The last two companies I worked for have used them in one way or another to centralize their knowledge, experiences, documentation and any other data that is vital for their work process.
I however use it to store my how-to's on Linux related experiences, manuals for appliances, documents of every nature like receipts, bills and much more but also recipes, travel information. This is one way to downsize on your ever growing pile of paper during your lifetime. I just threw away 6 garbage bags of paper.
The change to Confluence was largely due to the lack of search capability within Mediawiki. Of course you could install a plugin that enables a Lucene-based search within Mediawiki but I wanted more than the ability to just search through wiki's. Another great feature is the amazing plugins and extensions system within Confluence that can enrich any aspect. Some of them are retrieving RSS feeds, displaying recently changed items, showing popular labels, displaying navigational trees but you should check it out yourself.
One downside is that you will have to pay for a license to use Confluence apposed to Mediawiki which is completely free. However if you are using 10 or less users then it won't be that expensive.