The relationship between WordPress and Tumblr has always been pretty friendly: Tumblr's own blog used to be on WP, WordPress.com supports Tumblr as a Publicize option alongside Twitter and Facebook, our Akismet team sends them daily emails of splogs on the service, and there's healthy import and export traffic both ways.
Matt MullenwegAs the web becomes more and more of a part of our every day lives, it would be a horrible tragedy if it was locked up inside of companies and proprietary software.
Matt Mullenweg