It's very important for startups (and everybody else, for that matter) to learn from Facebook here. Straight to the point and I don't get the spammy(?) feeling I get from a lot of the other services I use. Great emails. (And I actually think I also have a 100% CTR on email from Facebook.)
Am I the only one who absolutely hates Facebook's email notifications? I turned them all off because I just don't care when someone tags me in a pic: to me that's just more spam.