Wikipedia also has an API (although this does little to address tptacek's concerns of database meltdown, unless you cache frequent requests):

http://en.wikipedia.org/w/api.php

http://www.mediawiki.org/wiki/API:Main_page

http://www.mediawiki.org/wiki/API:Query

For example:

http://en.wikipedia.org/w/api.php?action=query&prop=revi...

brings back:

   { 
     "query": { 
       "pages": {
         "1666533": {
           "pageid": 1666533, 
           "ns": 0, 
           "title": "Y Combinator (company)", 
           "revisions": [
             {
               "*": "{{Infobox company\n| company_name = Y Combinator\n 
                     [...redacted full wikitext content of article...]"
             }
           ]
         }
       }
     }
   }