On Moving From Tumblr to WordPress 

Ian Hines:

With the recent Tumblr downtime incident fresh in everyone’s minds a lot of folks have, understandably, been considering moving from Tumblr to WordPress. I’ve made that journey twice and I can tell you that it is possible to move your site from Tumblr to WordPress without any significant front-end changes.

This exhaustive, end-to-end guide is simply brilliant.