Wikia" and received $4 million in Series A funding. From the site:

Wikia are wiki communities creating free content with the MediaWiki software. These are hosted for free by Wikia, Inc., the company which runs the project. Anyone is free to start a new Wikia in accordance with the creation policy and terms of use. Wikia was founded by Angela Beesley and Jimmy Wales in October 2004. It celebrated its first birthday on November 2, 2005.

This is actually a great model. Think about it: these guys are making money simply by allowing others to create content for them. Nonetheless, I think we can all see the stumbling block: MediaWiki just isn't appealing for the average user. It's hard to use, unattractive and assumes some level of technical knowledge. What's more, the lack of focus will make monetization difficult (hosting a series of ProductWikis would be more profitable than hosting the full spectrum of topics). I'm also tempted to mention silos again, but I'm sure you can connect the dots on that one. Overall: good idea, but the strategy and execution are lacking.