Hey Paul,
I also tried out the Tumblr/Posterous debate, and have to admit that Posterous wins it for me. The simplicity of the application is awesome. I take loads of pics on my phone, so being able to mail it out, and get uploaded to 4 different services wins for me.
The only think I am waiting for now is the iPhone app, which is in development 🙂

Cheers
Marc