movabletype, textpattern, wordpress, mambo, joomla, drupal…it makes no difference.
free tagging, meta tags and keywords = miniscule to negligible effect on search engine placement.
SEF/human-readable URLS = no value to SEO; some value to repeat visitors; great value to site security and development of a well-organized site free from broken internal links.
title and description = critical to creating a SERP that people looking for your content will recognize as relevant
authentic, well-written content = the only thing. it’s the stuff you can control that most affects search engine placement and whether people visit your site.
well-written code / semantically valid xhtml that separates design from content = good for you, good for google.