It looks like a mailchimp targeted at developers. That said, it's not clear why I would use this over sendgrid or amazon's email service (better prices? easier API?)
That being said, there is definitely room for this type of service. I love the template language built in the emails.
Also I love your error page. Turns an "ehh" moment into an "aww" moment.
Not sure if the lack of markup is intentional - I like it. I can imagine a biz person saying "Could you add an image of a facebook logo in there?" and me saying "ummm... not really."