Mark Wilson says that category and tag listings in a blog should be disallowed in order to prevent duplicate content. I understand this. However, I want to put internal links on keywords in the blog posts to the tag and category pages in order for the readers to find more relevant content.I wonder whether putting those internal links to the category/tag pages which are disallowed in robots.txt is counted as useful from the perspective of SEO internal linking? 
To disallow indexing the category and tag listings in a blog
seo;links;robots.txt
Google Webmaster Central saysGoogle no longer recommends blocking  crawler access to duplicate content on  your website, whether with a  robots.txt file or other methods.So then I don't need to disallow crawling of category/tag listings in my blog. Duplicate content is penalized only when used for malicious purposes:In the rare cases in which Google  perceives that duplicate content may  be shown with intent to manipulate our  rankings and deceive our users, we'll  also make appropriate adjustments in  the indexing and ranking of the sites  involved. As a result, the ranking of  the site may suffer, or the site might  be removed entirely from the Google  index, in which case it will no longer  appear in search results.