This was a fantastic first post, Karma! Thanks for the great research and insights into both services. Ultimately, I would have to agree with your assessment. I’ve used both, and still have accounts on both services. For easy marketing engagement and quick photo and interest sharing posts, I definitely tend to angle toward Tumblr. Posterous is great for content-focused posts — though I find that my content posts tend to end up on wordpress blogs more often than not.