I like Tumblr too but let’s face it, the world is a better place because of WordPress. Now WP 3.3 gives you back the content that you own. I am not sure how bad it will hurt Tumblr but I believe it’s pretty big blow for them. For us it was really important to get back our content to control it and reuse it if needed. I hope it works…

"Because Tumblr's servers are often overloaded...". I bet they are now while we run this importer