Steve Rubel is considering to shift his popular blog from TypePad to WordPress - his main reason for considering WordPress over TypePad is the excellent Akismet spam catcher. [Related: Import Blogger into WordPress Blog]
Steve has a couple of options - leave all the old posts on TypePad and start afresh on WordPress or he hack transfer the archives from TypePad to WordPress and lose all the permalinks (and hence Google Juice)
Option A: Migrate all of the content and legitimate comments (the blog is unfortunately full of spam) over to Wordpress and lose all all permalinks.
Option B: Start fresh on Wordpress. This entails just moving the micropersuasion.com domain over. Under this scenario, the archives and all of the image links will remain here in tact for posterity but at the steverubel.typepad.com/micropersuasion URL (the “masked” domain). This too breaks all of the permalinks but at least leaves things in tact.
My suggestion - move the entire blog and comments from TypePad to WordPress and then use the following custom Permalink structur so you don’t lose any existing Google Juice.