I just got through reading a couple post (post1, post2) by brandontreb and I have to say I can't disagree more. I think Posterous is making some ballsy, yet positive moves. In the first post brandon outlines his thoughts on the "harsh blog post" that Posterous posted to lure users away from Tumblr.
This is just great marketing. Through careful word play they belittle Tumblr while building themselves up. They also discredit obvious features in the post, also again through careful word play, for instance "Email Posting The Works For Anyone". They never say that Tumblr doesn't have email posting, it does, they just say it doesn't "Work For Everyone". This is obviously an attempt to push their single address email posting system, where Tumblr generates a unique address for each blog.
Towards the bottom of the this article they mention a tool they have created that helps you easily move all your content from Tumblr to Posterous. They also have one for TwitPic. A mention of this is linked to in Brandon's second post. It seems that Posterous is doing so well and stealing so many people from TwitPic they got all uppity and decided to try to take the litigious route to whats looking like no avail.
I'm on Tumblr myself, but I think Posterous is killing it and other companies are starting to get scared. That is the sign of a quality product in my opinion. I eagerly await what happens next in this Posterous vs. The World debacle.