Well, I'm convinced. From now on I'll be using Posterous for my blogging needs. There are still a few things I'd like to see happening (keywords/tags, scheduled posting, css theming) but already this very clean system has captured me :-)
I do hope it will remain a clean, lean and smart system and not grow too much into a fat bulky CMS. But I think the intention of posterous is to remain lean&mean anyway.