Posterous did a good job with their email integration but to be honest I don't think most people want to update their blog with their email client.
Posterous really needs a UI/UX person. They are focusing too much on features. The basic flow of the site is confusing and IMO, the design is ugly.
Tumblr gets the evolution of blogs better than anyone out there. Most people want something in between wordpress and twitter. The "longform" blogs are starting to devolve into a weird ecosystem of stay at home moms and marketers who are trying to make money gaming google ads. I guess someone needs to serve this space, but it seems pretty 2nd rate and Wordpress already has it covered.
Short quotes, clips and photos are fun and where it's at. I'd be gunning for Tumblr before Wordpress. They do as good of a job for longer posts as anyone, anyway...