A wiki farm is a host for many wiki's. Sometimes they are commercial and charge a fee. An example is http://www.editme.com/. I am looking for one that hosts MediaWiki based Wikis.
I have a shared hosting website and have been unable to install MediaWiki on it. I probably could install it on a dedicated host, but that would cost $200/mo. Or I could buy a Linux based computer and use my DSL line. This would be slow, and I could not provide 24/7 support to make sure the system stayed up.
I don't know of a Mediawiki farm, but I don't see why a shared hosting environment would not work. Maybe you can post the problem you had here or the wikitech list.
There is a 4th option though besides shared hosting, dedicated hosting, and using your DSL line. You can run your own "virtual" linux box for around $20/month using User-Mode Linux (UML), but you'd need to know or learn about linux system administration. See this page: http://holton.ltc.vanderbilt.edu/wiki/UserModeLinux I'm using UML hosting to move my wiki and set up other wikis too. I'm hoping to switch to the MediaWiki engine if the memory & processor requirements aren't too steep.
-Doug
mediawiki-l@lists.wikimedia.org