I've not been able to find the reason yet, but search engines been indexing a lot of search results on Joomla sites. It seems to be an issue with the component itself, rather than any particular URL setup. I've been able to identify the issue with several different setups:

• Default Joomla URLs : /index.php?option=com_search&searchword=pursuing
• Default SEF URLs: /component/option,com_search/Itemid,38/index.php?searchword=ctores
• sh404SEF: /index.php/Search/newest-first.html?searchphrase=any&searchword=trip

I've not been able to find the reason yet, but its worth adding the search component to your robots.txt file. With the examples above, you would use this code:

• Default Joomla URLs: Disallow: /*com_search*/
• Default SEF URLs: Disallow: /*com_search*/
• sh404SEF: Disallow: /index.php/Search/

UPDATE: the answer is in the blog post. It's a Google bug.