The inevitable ruby style niggling, feel free to ignore: personally I like something a little more concise and inlined, some parts seem to have used more verbose idioms, (like Regexp.new instead of a literal), and also I think you need to escape the backreferences or use single quotes, something like:

  (words - @@nouns).each do |w|
      text.gsub!(/(\b)#{w}(\b)/i, '\1<span class="nurble">nurble</span>\2')
  end

EDIT: oops, backslash. Also, in the example, line 19, where you have 'sub', don't you mean 'pattern'?