I recommend to use Textpattern (http://www.textpattern.com), it is a very good system, and because of the XHTML and CSS usage it is great for SEs too. It could implement clean se friendly url’s, and the SEs could crawl every page it renders. It has a great community and a lot of plugin if you would like to use special features.
I used it in several projects and the only side-effect was high search engine ranking 