Despite the claims of email being dead and/or ripe for disruption, we all use it – a lot. And I agree that email is a great place to gain traction. There is a low barrier of entry by only requiring an email address to receive a newsletter, for instance. And there is no mystery how email works. The biggest thing may be the built in "stickiness." I enjoy trying out new web apps and services, but the hardest part about making an app useful is remembering to use it. That's not a problem if it ends up in a place I already have open and in front of me much of the day – my email.