> I'm not keen on changing any existing syntax.  But adding horizontal 
> rules and shortcut code for <pre><code> would be absolutely fine.

Where Markdown has plenty of ways to do the same thing, Textile seems 
to prefer one. So I think that should be the way forward. How about --- 
for a horizontal ruler? RDoc does that and it works in Markdown as 
well.

Maybe "cd." for a code block (<pre><code>)?

Also, it would be really nice if there was someway to have multiple 
paragraphs in both blockquotes and these new code blocks. Just like 
you've added with the lists. Perhaps if you space thrice (or more), 
just like with the lists, so:

bq. This is a blockquote with two paragraphs. Lorem ipsum dolor sit 
amet, consectetuer adipiscing elit. Aliquam hendrerit mi posuere 
lectus. Vestibulum enim wisi, viverra nec, fringilla in, laoreet vitae, 
risus.

     Donec sit amet nisl. Aliquam semper ipsum sit amet velit. 
Suspendisse id sem consectetuer libero luctus adipiscing.

becomes

<blockquote>
     <p>This is a blockquote with two paragraphs. Lorem ipsum dolor sit 
amet,
     consectetuer adipiscing elit. Aliquam hendrerit mi posuere lectus.
     Vestibulum enim wisi, viverra nec, fringilla in, laoreet vitae, 
risus.</p>

     <p>Donec sit amet nisl. Aliquam semper ipsum sit amet velit. 
Suspendisse
     id sem consectetuer libero luctus adipiscing.</p>
</blockquote>

The code blocks are a bit more tricky since the whitespace is 
significant. Markdown uses the "colon and everything starts at four 
spaces in"-style, but that doesn't really seem to be the Textile way. 
Perhaps two consecutive cd's could just be merged into one?

cd. WebserviceController
    before_filter :token_auth

cd. AdministrationController
    before_filter :ensure_login, :audit

becomes

<pre><code>
WebserviceController
    before_filter :token_auth

AdministrationController
    before_filter :ensure_login, :audit
</code></pre>

This could actually also work well for the blockquotes:

bq. This is a blockquote with two paragraphs. Lorem ipsum dolor sit 
amet, consectetuer adipiscing elit. Aliquam hendrerit mi posuere 
lectus. Vestibulum enim wisi, viverra nec, fringilla in, laoreet vitae, 
risus.

bq. Donec sit amet nisl. Aliquam semper ipsum sit amet velit. 
Suspendisse id sem consectetuer libero luctus adipiscing.

becomes

<blockquote>
     <p>This is a blockquote with two paragraphs. Lorem ipsum dolor sit 
amet,
     consectetuer adipiscing elit. Aliquam hendrerit mi posuere lectus.
     Vestibulum enim wisi, viverra nec, fringilla in, laoreet vitae, 
risus.</p>

     <p>Donec sit amet nisl. Aliquam semper ipsum sit amet velit. 
Suspendisse
     id sem consectetuer libero luctus adipiscing.</p>
</blockquote>
--
David Heinemeier Hansson,
http://instiki.nextangle.com/ -- A No-Step-Three Wiki in Ruby
http://www.basecamphq.com/    -- Web-based Project Management
http://www.loudthinking.com/  -- Broadcasting Brain