Requires the Tinder gem, and PHP on the server running MediaWiki must be compiled with --enable-sockets. The computer running the bot will also have to be open to the web - it can't be behind a firewall.

First, add this code to your MediaWiki LocalSettings.php, replacing the IP address with the IP of the server/computer running the bot, and the port to whatever you want to use (probably something above 40,000, but it's up to you):

$wgRC2UDPAddress = '69.178.6.244';
$wgRC2UDPPort = '41895';
$wgRC2UDPPrefix = "";

Now, you can run the bot! This is extremely hackish, because the retarded collective-mailing-list-coding system of the MediaWiki repos has somehow managed to code IRC color codes directly into their exported strings (at least with MediaWiki 1.2alpha, which is what I'm running right now).
You'll need to replace the new tinder definition with your subdomain on Campfire, the username and password with ones for the bot account you've created on your campfire room, and the room name with the room you want the updates to be sent to.

require 'rubygems'
require 'tinder'
require 'socket'
puts 'Dependencies loaded...'

campfire = Tinder::Campfire.new 'subdomain'
campfire.login 'email@domain.com', 'password'
exit unless room = campfire.find_room_by_name('Case Sensitive Room Name')
puts 'Campfire logged in...'

server = UDPSocket.new
exit unless server.bind('0.0.0.0', 41895)
puts 'Socket listening...'

loop do
  msg = server.recv(2048).gsub(/\003[\d]{0,2}/,'').chomp
  print "sending to room: #{msg.inspect}..."
  exit unless room.speak msg.to_s
  puts ' sent!'
end

This little bash script shows how to use curl, grep, tail, sed and perl one-liners in order to compose a bleeding-edge twitter bot.
This one returns daily weather forecasts for Lisbon city based on the BBC weather forecast rss feed.

#! /bin/sh

#Goto here
here=/home/guillaume/Personal
cd $here

#BBC Lisbon weather id
id=0048

#BBC weather RSS feed address
feed="http://feeds.bbc.co.uk/weather/feeds/rss/5day/world/${id}.xml"

#City
city=lisbon

#temporary file
file="weather${city}"

#Weather twitter bot
twitbot=weatherlisbon:*******

#Timestamp the log file
echo .>> $file.log
date >> $file.log

#Read the RSS feed and filter it
curl $feed | grep 'title' | tail -n 1 | perl -wlne'm/title>(.*)<\/title/i && print $1' | sed -e "s/&#xB0;//g" > $file.txt

#Read the forecast into a weather variable
read weather < $file.txt

#Twit the weather variable away
curl --basic --user $twitbot --data status="$weather" http://twitter.com/statuses/update.xml >> $file.log