hosted services

One of the things that cripples a small server running WordPress is SQL/disk scans, which require far more resources than simply serving pages from cache.

cache

I'm using BatCache, which communicates with Memcached to serve pages. Storing them on disk would probably be just as efficient, may even be a little better since there's less network layer involved, then Apache can just make a sendfile call to send a open fd to the client.

One thing you can do is to redirect search queries to a search engines' application, if you're bottle necking on disk/sql server resources.

rewrite

This can be done simply by doing the following in .htaccess:

RewriteCond %{REQUEST_URI} ^/wordpress/$
RewriteCond %{QUERY_STRING} ^s=(.*)$
RewriteRule ^ http://www.google.co.uk/search?q=site:usenix.org.uk+%1 [R=302,L]

The advantage of this is that if you have a popular site then you'll be able to leverage your popularity through google's index. The disadvantage is that your search responses may not be as recent as your posts.