You write. We share.
Blog from within Evernote. When done writing, just attach a -sharelephant tag to the note and it will be published on tumblr for you. In case you update that note later, changes will be reflected on tumblr automatically. In case a post is not of type text, sharelephant supports almost all tumblr types as described in the how-to.
Additionally, through the power of Evernote, you can share a notebook with co-workers and notes in there with the -sharelephant tag can be published to the company's blog. So there is no need to give away credentials or sending emails back and forth discussing how posts should look like.
Furthermore, one can now carry a full searchable offline blog backup around, so it is easy to check some facts in posts which have been written a while back if on the plane for example.
What are you waiting for, head over to sharelephant.com and give it a try. It is free after all.