All In One SEO does the job very well, by simply adding a "noindex,follow" to archive and category pages.
If excluding categories is the right approach depends alot on the structure of your blog. If you are posting alot, using all different categories, it's less of a problem than categories always used together.
E.g., if most of your "pornstar" category posts are in "big tits" and "hardcore" as well, it's not that good. If there is alot of variety, keep the categories indexed.