Dynamic URLs can impede the search engine spiders from fully spidering and indexing your blog. Err on the side of caution and use “rewritten” URLs. The excellent (and free!) blogging software WordPress supports URL rewriting, so you can have nice, search engine friendly URLs. Better still, the WordPress URLs contain hyphens rather than underscores (like TypePad uses), since underscores are not considered to be word separators by Google. If you ever switch blog platforms, it’s imperative that the old permalink URLs still work. That’s because there will be numerous deep links into specific post pages in your blog from other bloggers, and that provides your blog with that all-important “link gain” (e.g. Google’s PageRank). You wouldn’t want to lose that! Recently we assisted BusinessBlogConsulting.com with the conversion from TypePad to WordPress 2.0. As part of the migration, we ensured that the new WordPress permalink URLs were consistent with the old TypePad permalink URLs. That means that the old posts still have underscores in them. However, for new posts, the permalink URLs will contain full words and hyphens not underscores. If for some reason you have to change the URLs, then at least redirect the old URLs to the new ones, and make sure you do it as a permanent (301 style) redirect. That way the link gain passes on to the new URL. Also make sure you 301 redirect requests for pages from your domain without the www (e.g. http://businessblogconsulting.com/category/adverblogs/) to the corresponding page on your www URL (e.g. http://www.businessblogconsulting.com/category/adverblogs/). This will eliminate duplicate pages in the search engine indices and consolidate link gain. Otherwise when people link to http://businessblogconsulting.com without the www it creates another site for the search engines to visit and explore.