Why I switched from Wordpress to Posterous
Easy custom domains
Setting up duncankinney.com (my former photography portfolio site with Livebooks) to point to Posterous was an easy three step process. It was even more complicated than it had to be because I was set up with GoDaddy. Another bonus, no hosting fees.
Simplicity
The format is so simple that I can definitely see myself getting back into the swing of more quote and comment style blogging. While I don't see myself blogging from email I could if I ever wanted to.
Fast
It's so lightweight and there are so few things to worry about compared to my old Wordpress blog that it's way, way faster.